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SUMMARY:Whether the Hypothesis of Conformal Invariance Is Fulfilled Near t
 he Critical Points of Fluids?
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UID:indico-contribution-18-565@indico.bitp.kiev.ua
DESCRIPTION:Speakers: A.V. Chalyi (Bogomolets National Medical University)
 \nL.A. Bulavin$^{1\,2}$\, E.G. Rudnikov$^{1\,3}$\, K.O. Cherevko$^{1\,2}$\
 , A.V. Chalyi$^4$\n\n1 Department of Molecular Physics\, Faculty of Physic
 s\, Kyiv National Taras Shevchenko University\, Volodymyrska Str.\, 64 Kyi
 v 01601\, Ukraine\n2 Institute for Safety Problems of Nuclear Power Plants
  of the NAS of Ukraine\, Lysohirska Street\, 12\, Kyiv 03028\, Ukraine\n3 
 Department of Biomedical Cybernetics\, Faculty of Biomedical Engineering\,
  National Technical University of Ukraine "Ihor Sikorsky Kyiv Polytechnic 
 Institute"\, Beresteyskiy Ave.\, 37 Kyiv 03056\, Ukraine\n4 Department of 
 Medical and Biological Physics and Informatics\, Bogomolets National Medic
 al University\, Shevchenko Blvd.\, 13\, Kyiv 01601\, Ukraine\n\n\nConforma
 l transformations were introduced in the physics of phase transitions by A
 .M. Polyakov [1]. Based on the hypothesis of conformal invariance (CI)\, s
 cale invariance with anomalous dimensions was proposed [2]\, both in the t
 heory of critical phenomena for fluctuating quantities and in hadronic int
 eractions. The CI hypothesis also proves to be fundamental in interdiscipl
 inary research\, for example\, to explain the formation of hexagonal struc
 tures in the system of grid cells in the brain (2014 Nobel Prize in Physio
 logy and medicine) [3] An important consequence of CI hypothesis in the ph
 ysics of phase transitions\, according to [4]\, is the orthogonality relat
 ion for two fluctuating quantities of transitions with different scale dim
 ensions within the algebra of fluctuating quantities\, which was proposed 
 by V.L. Pokrovskii [5] (see also [6]). The aim of this work is to verify f
 or the first time the CI hypothesis for the liquid-vapor critical points o
 f single-component fluids based on existing experimental data. For this pu
 rpose\, we used experimental data for carbon dioxide [7]\, water [8\,9]\, 
 and polyol ester (POE9) lubricant with a higher critical temperature\, for
  which experimental data are available in the scientific literature [10]. 
 These fluids have critical temperatures $T_C=304.1$K\, $T_C=647.1$ K and $
 T_C=970.0$ K and critical densities  $\\rho_C=467.6$ kg/m3\, $\\rho_C=322.
 0$ kg/m3 and  $\\rho_C=220.3$ kg/m3\, respectively. It was proven that for
  the studied fluids the hypothesis of conformal invariance holds in temper
 ature intervals determined from experimental data near their liquid-vapor 
 critical points. The values of the temperature intervals in which the hypo
 thesis of conformal invariance near the liquid-vapor critical points is fu
 lfilled depend on the absolute values of the critical parameters of the st
 udied fluids. Confirmation of the CI hypothesis also means that the temper
 ature derivative of the coexistence-curve diameter retains the weak singul
 arity with the exponent of the isochoric heat capacity [11-13].\n\n1. A.M.
  Polyakov\, Conformal symmetry of critical fluctuations\, JETP Lett. 12\, 
 381–383 (1970).\n2. A.A. Migdal\, Conformal invariance and bootstrap\, P
 hys. Lett. B 37(4)\, 386–388 (1971). doi: 10.1016/0370-2693(71)90211-5\n
 3. A.V. Chalyi. What is Medicine? Basic Principles of Physics in Medicine 
 and Beyond\, Springer Nature Switzerland AG (2024). https//doi.org/10/1007
 /978-3031-64979-0\n4. L.P. Kadanoff\, Operator algebra and the determinati
 on of critical indices\, Phys. Rev. Lett. 23(25)\, 1430–1433 (1969).\n5.
  V.L. Pokrovskii\, Feasibility of experimental verification of the conform
 al invariance hypothesis\, JETP Lett. 17\, 219–221 (1973).\n6. A.Z. Pata
 shinsky\, V.L. Pokrovsky\, Fluctuation Theory of Phase Transitions (Pergam
 on Press\, Oxford\, 1979).\n7. R. Span\, W. Wagner\, Equations of state fo
 r technical applications. III. Results for polar fluids\, Int. J. Thermoph
 ys. 24(1)\, 111–162(2003). doi: 10.1023/A:1022362231796\n8. M.Z. Southar
 d\, D.W. Green\, Perry’s Chemical Engineers’ Handbook\, 9th ed. (McGra
 w-Hill Education\, New York\, 2019).\n9. REFPROP Database\, National Insti
 tute of Standards and Technology\, SRD 23\, Version 10 (2018). doi: 10.184
 34/T4/1502528\n10. T.J. Bruno\, T.J. Fortin\, M.L. Huber\, A. Laesecke\, E
 .W. Lemmon\, E. Mansfield\, M.O. McLinden\, S.L. Outcalt\, R.A. Perkins\, 
 K.N.Urness\, J.A. Widegren\, Thermophysical Properties of Polyol Ester Lub
 ricants\, NISTIR 8263 (National Institute of Standards and Technology\, 20
 19). doi: 10.6028/NIST.IR.8263\n11. L.M. Artyukhovskaya\, E.T. Shmanskaya\
 , Yu.I. Shimanskii\, Heptane coexistence curve near the critical point. JE
 TP 63(3)\, 2153-2164\, (1972).\n12.  L.A. Bulavin\, Yu.I. Shimanskii. The 
 singularity of the coexistence-curve diameter of ethane. JETP Lett 29(8) 4
 82 (1979).\n13. A.V. Chalyi\, L.A. Bulavin\, K.A. Chalyy. On the neutron o
 ptics of liquids\, J/ Mol. Liquids 383\, 121979 (2023).\,\n\nhttps://indic
 o.bitp.kiev.ua/event/18/contributions/565/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/565/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Field-controlled thermal spin transport in rutile-type altermagnet
 s
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UID:indico-contribution-18-553@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yuliia Gusieva (G.V. Kurdyumov Institute for Metal P
 hysics of the NAS of Ukraine)\nThe magnon-driven transport properties of a
  two-dimensional model of a $d$-wave altermagnet are investigated. As a ca
 se study\, we consider a rutile with easy-planar anisotropy (e.g.\, $\\mat
 hrm{NiF}_2$)\, where the sublattice magnetization vectors lie within the $
 xy$-plane in the equilibrium state. An external magnetic field is applied 
 perpendicular to this plane\, along the $z$-axis. The model Hamiltonian ac
 counts for anisotropy\, Zeeman interaction\, and the complex structure of 
 the Heisenberg exchange\, including ferromagnetic\, antiferromagnetic\, an
 d specific altermagnetic exchange contributions.\n\nWe computed the spectr
 um of spin waves and found that altermagnetism renders magnons chiral\, as
  in the case of the easy-planar $g$-wave altermagnets [1]. The altermagnet
 ically-induced magnon magnetic moment is $k$-dependent\, and its distribut
 ion over the 1st Brillouin zone possesses $d$-wave symmetry for each magno
 n branch. The latter results in a magnon-driven spin current in response t
 o an applied temperature gradient\, similar to that in easy-axial $d$-wave
  altermagnets [2]. The corresponding tensor of the thermal spin conductivi
 ty $\\sigma_{\\alpha\\beta}$ was derived from the transport Boltzmann equa
 tion within the relaxation time approximation. The direction of the spin c
 urrent is determined by the direction of the temperature gradient relative
  to the crystallographic axes (Fig. 1). An important finding of this resea
 rch is the possibility of controlling the spin conductivity by the applied
  magnetic field. We observe that at low temperatures\, the conductivity is
  governed by the lowest-energy magnon mode\, and its temperature dependenc
 e follows a $T^2$-law. However\, for high temperatures\, $\\sigma_{\\alpha
 \\beta}$ is temperature-independent\, and its value and sign are determine
 d by the magnetic field. The field-controlled spin conductivity highlights
  the potential for tunable magnonic and spin-caloritronic devices\, provid
 ing a robust mechanism for controlling spin and heat currents at the nanos
 cale.\n\n**Fig. 1.** Temperature dependencies of $\\sigma_{xy}$ for differ
 ent values of the reduced magnetic field $b = B_z / B_{\\mathrm{sf}}$\, wh
 ere $B_{\\mathrm{sf}}$ is the critical spin-flip field.\n\nThis work was s
 upported by the German Federal Ministry of Research\, Technology and Space
  (BMFTR) through the GU-QuMat project (01DK24008).\n\n[1] V.P. Kravchuk\, 
 et al.\, *Phys. Rev. B*\, **112**\, 144421 (2025).  \n[2] K.V. Yershov\, e
 t al.\, *Phys. Rev. B*\, **110**\, 144421 (2024).\n\nhttps://indico.bitp.k
 iev.ua/event/18/contributions/553/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/553/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum Computing Study of the Speed of Quantum Evolution in the I
 sing Model in a Longitudinal Magnetic Field
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UID:indico-contribution-18-546@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Markiian Kachmar (Professor Ivan Vakarchuk Departmen
 t for Theoretical Physics\, Ivan Franko National University of Lviv)\nThe 
 speed of quantum state evolution is a fundamental characteristic of quantu
 m dynamics. As shown in [1]\, for pure quantum states\, it is directly gov
 erned by energy fluctuations. In the present work\, we examine the speed o
 f quantum evolution in a spin system described by the Ising model and subj
 ected to a longitudinal magnetic field. We perform analytical derivations 
 and quantum computing using AerSimulator. The quantum programming of the s
 peed of quantum evolution employs two distinct approaches: the estimation 
 of the expectation value of the evolution operator for short times and the
  direct measurement of Pauli correlators [2]. The results of the quantum c
 omputations are in agreement with the theoretical results. We also show th
 at the quantum states evolved in spin systems described by the Ising model
  in a magnetic field can be treated as quantum graph states representing v
 ertex- and edge-weighted graphs. We establish relations between the speed 
 of quantum evolution and the structural properties of the graph.\n[1] A. S
 himony\, Ann. N.Y. Acad. Sci. 755\, 675-679 (1995). doi: 10.1111/j.1749-66
 32.1995.tb39008.x .\n[2] Kachmar\, M.\, and Kh Gnatenko. (2025). Visnyk Lv
 iv Univ.\, Ser. Phys. 62\, 67–74 (2025). doi: 10.30970/vph.62.2025.67\n\
 nhttps://indico.bitp.kiev.ua/event/18/contributions/546/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/546/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Low-order momentum correlation functions of the symmetric Tamm-Dan
 coff $q$-bosons\, derived via under-trace operations
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UID:indico-contribution-18-556@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yuriy Mishchenko (Bogolyubov Institute for Theoretic
 al Physics of NAS of Ukraine)\n$\\quad$Using the set of independent Symmet
 ric Tamm-Dancoff (STD) type $q$-deformed quantum oscillators [1] with the 
 standard linear-in-$N$ Hamiltonian\, we construct respective gas of $q$-bo
 sons. Such a deformed $q$-Bose gas model admits [2] exact analytic express
 ions for the $r$-particle momentum correlation function\, and correspondin
 g intercepts\, of any $r$th order. This is the third example of deformed o
 scillators' based Bose gas model\, along with the $qp$-Bose gas model [3] 
 and the $\\mu$-deformed one [4] (based on Jannussis's oscillator)\, where 
 correlation average $\\langle (a^\\dagger_{\\bf k})^r (a_{\\bf k})^r \\ran
 gle$ was calculated explicitly. In view of the formal resemblance between 
 the $qp$-bracket and the STD deformation structure function\, with $N$-mul
 tiplier ignored\, we apply the idea of the derivation from [3] for $qp$-bo
 sons\, to the current case of STD $q$-bosons.\n\n$\\quad$Indeed\, using ju
 st under-trace algebraic operations\, for the STD $q$-bosons in a fixed $\
 \bf k$-mode we find\n$\\qquad\\qquad \\langle a^\\dagger a\\rangle_\\mathr
 m{STD}\n=  \\frac1{(e^{\\beta\\omega} -\\\, q)^2}\\\,\n\\biggl\\{\\\n \\Bi
 gl\\langle\n  \\frac{\\bigl[a\, [a\,a^\\dagger]_q \\bigr]_q\\\, a^\\dagger
 }{\\varphi_\\mathrm{STD}(N+1)}\n \\Bigr\\rangle\n    + \\frac{ [1]^\\mathr
 m{STD}_q!\\\, e^{\\beta\\omega} }{\\mathrm{Tr}\\\, e^{-\\beta\\omega N}}\n
  \\biggr\\}$\nversus $\\langle a^\\dagger a\\rangle_{qp} =  \\frac{[1]_{qp
 }!}{e^{\\beta\\omega}\\\,-\\\,q}\n\\\, \\bigl\\langle[a\,a^\\dagger]_q\\bi
 gr\\rangle$ for $qp$-bosons\, see [3]. What concerns the quadratic correla
 tions\, using the same approach of under-trace transformations we derive\n
 $\\qquad \\bigl\\langle a^{\\dagger2}a^2 \\bigr\\rangle_\\mathrm{STD}\n =\
 n\\frac1{(e^{\\beta\\omega} -\\\, q^2)^3 (e^{\\beta\\omega} -\\\, 1)^3}\\\
 n\\biggl\\{\\\n\\Bigl\\langle \\ \n  \\sum\\limits_{i=0}^4 A_i(q)\\\; \\te
 xtrm{g}_q(N\\!+\\!1\\!+\\!i)\\\,\\textrm{g}_q(N\\!+\\!i)\n         \\cdot 
 q^{-2N} \\Bigr\\rangle$\n$\\qquad\\qquad\\qquad\\qquad\n-\\  (e^{\\beta\\o
 mega}-1)\\\, \\textrm{g}_q(0) P_2\\bigl(q\;e^{\\beta\\omega}\\bigr)\n\\big
 gr\\}\\\n  +\\\n\\varphi_\\mathrm{STD}(2)! \\frac{e^{\\beta\\omega}-\\\,1}
 {(e^{\\beta\\omega}\\\,-\\\,q^2)^3}$\nwhere underlying role belongs to the
  double commutator as well\, through $\\textrm{g}_q(N)$-function\, $[a\,[a
 \,a^\\dagger]_q]_q = - \\textrm{g}_q({N+1})\\\, q^{1-N} \\cdot a$\,  and $
 P_2(q\;e^{\\beta\\omega})$ is some quadratic polynomial in $e^{\\beta\\ome
 ga}$\, with coefficients depending on $q$.\n\n 1. W.S. Chung\, A.M. Gavril
 ik\, I.I. Kachurik\,\n    A.P. Rebesh: J. Phys. A: Math. Theor. **47**\, 3
 05304 (2014).\n 2. A.M. Gavrilik\, Yu.A. Mishchenko\, arXiv preprint\,\n  
   arXiv:1410.0538  (2014).\n 3. L.V. Adamska\, A.M. Gavrilik\, J. Phys. A:
  Math. Gen.\n    **37**\, 4787-4796 (2004).\n 4. A.M. Gavrilik\, Yu.A. Mis
 hchenko\, Phys. Lett. A\n    **376**\, 2484-2489 (2012).\n\nhttps://indico
 .bitp.kiev.ua/event/18/contributions/556/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/556/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Symmetry analysis and exact solutions of a model describing viscou
 s fingering induced by a chemical reaction
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UID:indico-contribution-18-519@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Vasyl' Davydovych (Institute of Mathematics\,  NAS o
 f Ukraine)\nWe study a mathematical model describing viscous fingering ind
 uced by the chemical reaction $A+B \\to C$\, introduced in [T. Gerard and 
 A. De Wit\, Phys. Rev. E\, 2009]. The model couples the concentrations of 
 the reactants\, $u(t\,x\,y)$ and $v(t\,x\,y)$\, and their product\, $w(t\,
 x\,y)$\, with the pressure $p(t\,x\,y)$ and the two-dimensional velocity f
 ield $U=(U_1\,U_2)$\, and is given by \n\n$ \\nabla\\cdot U=0\,  \\\n\\kap
 pa \\nabla p=-\\mu(w)U\,  \\\nu_t+ U\\cdot\\nabla u = d_1 \\triangle u-kuv
 \,  $\n$v_t+ U\\cdot\\nabla v = d_2 \\triangle v-kuv\,  \\\nw_t+U\\cdot\\n
 abla w = d_3 \\triangle w+kuv.$\n\nThe above system is investigated by mea
 ns of the classical Lie symmetry approach. A Lie symmetry classification i
 s obtained for different parameter cases\, and the resulting symmetries ar
 e used to construct exact solutions. In the case of radially symmetric str
 eam functions\, several families of exact solutions are derived. These sol
 utions make it possible to analyze the evolution of the reactant and produ
 ct concentrations in both space and time and provide an analytical descrip
 tion of the corresponding viscous-fingering dynamics.\n\nThe presented res
 ults were obtained in collaboration with R. M. Cherniha.\n\nhttps://indico
 .bitp.kiev.ua/event/18/contributions/519/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/519/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Representations of solutions for a first order quasilinear equatio
 n in a form of series in powers of the copolynomial δ-function
DTSTART;VALUE=DATE-TIME:20260922T143500Z
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DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-516@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Roman Skurikhin (V. N. Karazin Kharkiv National Univ
 ersity)\nBy a *copolynomial* we mean here a linear functional on the space
  of polynomials $\\mathbb{R}[x]$. The space of copolynomials is denoted by
  $\\mathbb{R}[x]'$. If $T\\in\\mathbb{R}[x]'$ and $p\\in\\mathbb{R}[x]$\, 
 then the result of application of $T$ to $p$ is written as $(T\,p)$. The d
 erivative $T'$ of a copolynomial $T\\in\\mathbb{R}[x]'$ is defined in the 
 same way as in the classical theory of generalized functions: $(T'\,p)=-(T
 \,p')$\, $p\\in\\mathbb{R}[x]$. An important example of a copolynomial is 
 the $\\delta$-function\, which is defined by $(\\delta\,p)=p(0)$\, $p\\in\
 \mathbb{R}[x]$.\n\nThe *Cauchy-Stieltjes transform* of a copolynomial $T\\
 in\\mathbb{R}[x]'$ is defined as the following formal Laurent series in th
 e ring $s^{-1}\\mathbb{R}[[s^{-1}]]$: $C(T)(s)=\\sum_{k=0}^{\\infty}(T\,x^
 k)/s^{k+1}$. The mapping $C:\\mathbb{R}[x]'\\to s^{-1}\\mathbb{R}[[s^{-1}]
 ]$ is an isomorphism of these vector spaces. The multiplication of copolyn
 omials is defined through the multiplication of their Cauchy-Stieltjes tra
 nsforms. The theory of linear and nonlinear PDEs in the ring $\\mathbb{R}[
 x]'[[t]]$ was studied in [1\,2]\, respectively.\n\nLet $f(z)=\\sum_{j=1}^{
 \\ell}f_jz^j\\in\\mathbb{R}[z]$. We prove that the following Cauchy proble
 m for the first order quasilinear equation\n\n$$\n\\frac{\\partial u}{\\pa
 rtial t}+f(u)\\frac{\\partial u}{\\partial x}=0\,\n\\qquad u(0\,x)=\\delta
 (x)\,\n$$\n\nin $\\mathbb{R}[x]'[[t]]$ has a unique solution\n\n$$\nu(t\,x
 )=\\sum_{k=0}^{\\infty}\\sum_{|\\alpha|=k}\nf_1^{\\alpha_1}\\ldots f_{\\el
 l}^{\\alpha_{\\ell}}\n\\frac{\\left(\\sum_{j=1}^{\\ell}j\\alpha_j+k\\right
 )!}\n{\\alpha_1!\\ldots\\alpha_{\\ell}!\n \\left(\\sum_{j=1}^{\\ell}j\\alp
 ha_j+1\\right)!}\n\\delta^{\\sum_{j=1}^{\\ell}j\\alpha_j+k+1}(x)t^k\,\n$$\
 nwhere $\\alpha=(\\alpha\\_1\,\\ldots\,\\alpha_{\\ell})\\in\\mathbb{N}\\_0
 ^{\\ell}$ is a multi-index\, $|\\alpha|=\\sum\\_{j=1}^{\\ell}\\alpha\\_j$.
 \n\n*Acknowledgement.* Roman Skurikhin was supported by the National Resea
 rch Foundation of Ukraine\, project No. 2025.07/0369 “Qualitative method
 s of nonlinear analysis of heterogeneous structures”.\n\n[1] Gefter S. L
 .\, Piven' A. L.: Partial differential equations in module of copolynomial
 s over a commutative ring\, *J. Math. Phys. Anal. Geom.* **21** (2025)\, N
 o. 1\, 56–83.\n\n[2] Gefter S. L.\, Piven' A. L.: Nonlinear Partial Diff
 erential Equations in Module of Copolynomials over a Commutative Ring. *J.
  Math. Phys. Anal. Geom.* **21** (2025)\, No. 3\, 319–345.\n\nhttps://in
 dico.bitp.kiev.ua/event/18/contributions/516/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/516/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The some solution of the Bryan-Pidduck equation
DTSTART;VALUE=DATE-TIME:20260922T143000Z
DTEND;VALUE=DATE-TIME:20260922T143500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-513@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksii Hukalov (B.Verkin Institute for Low Temperat
 ure Physics and Engineering of the NAS of Ukraine)\nThe Boltzmann equation
  [1] that describes the evolution of rarefied gases is one of the main equ
 ations of the kinetic theory of gases. For a model of rough spheres\, the 
 equation has the form:\n\\begin{equation}\nD(f)= Q(f\,f)\,\n\\end{equation
 }\nwhere the left-hand side of the equation is the  differential operator:
 \n$$ D(f)\\equiv\\frac{\\partial f}{\\partial t}+\\left(V\,\\frac{\\partia
 l f}{\\partial x}\\right)\,$$\nand the right-hand side of the Boltamann eq
 uation  is the collision integral\, which for the hard spheres model is as
  follows:\n$$Q(f\,f)\\equiv\\frac{d^{2}}{2}\\int_{R^{3}}\\!\\!\\!dV_{1} \\
 int_{R^{3}}\\!\\!\\!d\\omega_{1} \\int_{\\Sigma} d\\alpha B(V-V_{1}\,\\alp
 ha)\\Bigl[f(t\,V_{1}^{*}\,x\,\\omega_{1}^{*})f(t\,V^{*}\,x\,\\omega^{*})-f
 (t\,V\,x\,\\omega)f(t\,V_{1}\,x\,\\omega_{1})\\Bigl]\,$$ where $f(t\,V\,x\
 ,\\omega)$ is the distribution function of particles.\n\nThe problem of de
 termination of the exact and approximate solutions of the Boltzmann equati
 on in the explicit form is quite urgent. At present\, the sole known exact
  solution of the Boltzmann equation is an expression usually called the Ma
 xwell distribution or simply Maxwellian (after J. C. Maxwell\, Scottish ph
 ysicist). In the case of Maxwellians $M$\, we get\n\\begin{equation}\nD(f)
 =0\, \\quad  Q(f\,f)=0.\n\\end{equation}\n\nThe solution to this equation 
 will be look for in the next form:\n$$ f(t\,x\,V\,\\omega)=\\sum\\limits_{
 i=1}^{\\infty}\\varphi_i(t\,x)M_i(t\,x\,V\,\\omega).$$\n\nAs a measure of 
 the deviation between the parts of the Boltzmann equation we will consider
  a uniform-integral error of the form:\n$$\\Delta=\\sup_{(t\,x)\\in \\math
 bb{R}^4}\\int_{\\mathbb{R}^3}dV \\int_{\\mathbb{R}^3}d\\omega\\Big|D(f)-Q(
 f\,f)\\Big|.\n$$\n\nIn the paper[2]\, we were obtained sufficient conditio
 ns for the coefficient functions and hydrodynamic parameters appearing in 
 the distribution\, which enable one to make the analyzed error as small as
  desired.\n\n**REFERENCES**\n\n[1] S. Chapman and T.G. Cowling. The Mathem
 atical Theory of Non-Uniform Gases. *Cambridge Univ. Press\,* Cambridge\, 
 1952.\n\n[2] V. Gordevskyy and O. Hukalov\; The Interaction of a Countable
  Number of Eddy Flows for the Bryan-Pidduck Model. *J. Math. Phys. Anal. G
 eom.* 2025\, 21\, 218-231.\n\nhttps://indico.bitp.kiev.ua/event/18/contrib
 utions/513/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/513/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A Hypercomplex method of solving the piecewise-continuous Dirichle
 t problem for the Lamé system
DTSTART;VALUE=DATE-TIME:20260922T142500Z
DTEND;VALUE=DATE-TIME:20260922T143000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-509@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Serhii Gryshchuk (Institute of Mathematics of NAS of
  Ukraine\, Zhytomyr Military Institute named after S.P. Korolyov)\nA hyper
 complex method for solving the piecewise-continuous Dirichlet problem for 
 the Lamé system in domains with corner points has been developed\, which 
 is based on the representation of solutions using the components of a mono
 genic function in a commutative biharmonic algebra. Using a biharmonic int
 egral of the Cauchy type\, the Dirichlet problem has been reduced to a sys
 tem of integral equations.\n              References\n[1] Serhii Gryshchuk
 \, Sergiy Plaksa\, Piecewise-continuous Dirichlet problem for Lam\\'{e} sy
 stem\, Ukr. mat. visnyk\, Vol. 23\, No. 2\, pp. 171-200 (2026).\n\nhttps:/
 /indico.bitp.kiev.ua/event/18/contributions/509/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/509/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Effect of fluorination on the molecular electrostatic potential of
  itic non-fullerene acceptors
DTSTART;VALUE=DATE-TIME:20260922T142000Z
DTEND;VALUE=DATE-TIME:20260922T142500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-537@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Mariia  Terebinska (Chuiko Institute of Surface Chem
 istry\, NAS of Ukraine)\nOrganic solar cells based on non-fullerene accept
 ors (NFAs) are a promising direction in the development of organic photovo
 ltaics due to the possibility of targeted molecular design and control of 
 their electronic and optical properties. Particular attention is paid to A
 –D–A-type acceptors\, including ITIC and its fluorinated derivatives\,
  for which the introduction of fluorine atoms provides an effective approa
 ch to modifying the electronic structure and electron-accepting properties
  of the molecules. In this work\, a quantum-chemical study of ITIC\, ITIC-
 2F\, and ITIC-4F molecules was performed using density functional theory (
 DFT) and time-dependent DFT (TD-DFT). Geometry optimizations were carried 
 out at the B3LYP/6-31G(d\,p) level\, followed by analysis of the electroni
 c structure\, frontier molecular orbitals (HOMO/LUMO)\, and molecular elec
 trostatic potential (MEP). It was found that sequential fluorination has a
  negligible effect on the molecular geometry. All studied systems retain a
 n almost planar π-conjugated structure\, with changes in the dihedral ang
 les not exceeding 0.12°. This indicates that the effect of fluorination o
 n the electronic properties is governed predominantly by electronic rather
  than structural factors.\nAnalysis of the frontier molecular orbitals sho
 wed that the HOMO is predominantly localized on the central donor IDTT cor
 e\, whereas the LUMO is mainly concentrated on the terminal acceptor fragm
 ents. Upon going from ITIC to ITIC-4F\, the HOMO energy decreases from −
 5.380 to −5.508 eV\, while the LUMO energy decreases from −3.309 to 
 −3.464 eV. The stabilization of the LUMO is more pronounced and is attri
 buted to the electron-withdrawing inductive effect of the fluorine atoms. 
 Particular attention was paid to the analysis of the molecular electrostat
 ic potential. The MEP maps show that\, for ITIC\, ITIC-2F\, and ITIC-4F\, 
 the most negative electrostatic potential is predominantly localized on th
 e terminal electron-accepting fragments\, particularly near the carbonyl g
 roups. In contrast\, the central conjugated core is characterized by a pre
 dominantly neutral or weakly positive potential.\nFluorination does not al
 ter the overall topology of the MEP distribution but systematically affect
 s its local intensity. For ITIC-2F\, an increase in the negative electrost
 atic potential is observed in the terminal acceptor regions\, while this e
 ffect becomes more pronounced for ITIC-4F. At the same time\, the central 
 part of the molecule becomes more positive\, indicating enhanced intramole
 cular polarization and redistribution of electron density from the central
  conjugated core toward the peripheral acceptor fragments.\nThus\, the MEP
  analysis (fig.) is consistent with the spatial distribution of the LUMO a
 nd confirms an enhanced electron-accepting character of the peripheral fra
 gments upon fluorination. The observed modification of the electrostatic p
 olarization may affect the nature of intermolecular interactions and charg
 e-transfer processes in ITIC-based molecular materials. The most pronounce
 d changes are observed for ITIC-4F containing four fluorine atoms.\n 	 	 \
 nFig. MEP mapped onto an electron density isosurface (ρ = 0.001 a.u.) for
  ITIC\, ITIC-2F\, and ITIC-4F molecules.\n\nhttps://indico.bitp.kiev.ua/ev
 ent/18/contributions/537/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/537/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum chemical study of methanol interaction with a pyrene-based
  acid
DTSTART;VALUE=DATE-TIME:20260922T141500Z
DTEND;VALUE=DATE-TIME:20260922T142000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-552@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oksana Kremen (Chuiko Institute of Surface Chemistry
  of National Academy of Sciences of Ukraine)\n**Quantum chemical study of 
 methanol interaction with a pyrene-based acid**\n\n*Kremen O. S.1\, Bychko
  I. B.2\, Nikolaienko T.Y.3\, Lobanov V. V.1\, Strizhak P. E.2*\n\n1Chuiko
  Institute of Surface Chemistry of the NAS of Ukraine\, \nOleh Mudrak Str.
 \, 17\, Kyiv-03164\, Ukraine\, kremenoksana@ukr.net\n2L. V. Pisarzhevskii 
 Institute of Physical Chemistry of the NAS of Ukraine\, \nProspect Nauki\,
  31\, Kyiv-03028\, Ukraine\n3Taras Shevchenko National University of Kyiv\
 , Faculty of Physics\, \nVolodymyrska Str.\, 64/13\, Kyiv 01601\, Ukraine*
 \n\nThe conversion of methanol (MeOH) to dimethyl ether (DME) is a large-s
 cale industrial process\, and developing advanced catalysts to reduce cost
 s is important. Oxygen-containing carbons are promising metal-free catalys
 ts for many reactions\; therefore\, this report presents quantum-chemical 
 calculations (DFT\, M062X/6-31G**/D3\, ORCA 6.0.0) of the interaction betw
 een MeOH and pyrene-based acid (Pyr) in the gas phase at T = 0 K to elucid
 ate the initial interaction mechanism for further investigation of the Met
 hanol-to-DME conversion.\n\nGeometry optimisation yielded two acid isomers
  (A and B)\, depending on the orientation of the –COOH group plane relat
 ive to the aromatic plane. The –COOH group was covalently bonded to the 
 terminal hexagonal carbon atom (alpha carbon) of the Pyr molecule (instead
  of a hydrogen atom) in the so-called syn conformation (where the O=C–O
 –H dihedral angle (θ) is defined to be 0°). Isomer A has a more twiste
 d –COOH group relative to the aromatic core (θ=19.96°) than isomer B (
 θ=0.82°)\, due to the asymmetry of the carbon skeleton. The total energy
  of the planar B-Pyr acid is lower by 5.95 kJ/mol than that of the twisted
  A-Pyr acid molecule.\n\nBader's Quantum Theory of Atoms in Molecules was 
 used to identify the presence or absence of intramolecular hydrogen bonds 
 (HB) in Pyr. The topological analysis of the electron density distribution
  confirmed the presence of two intramolecular HBs in the B-Pyr (between O 
 atoms of the –COOH group and H atoms of the aromatic core)\, as evidence
 d by the presence of the corresponding bond critical points (BCPs) of type
  (3\, −1). In contrast\, only a single intramolecular HB was observed in
  the A-Pyr acid (between the O atom of the –OH group and the hydrogen at
 om of the aromatic core). Despite the C=O···H–C length being 2.361 Å
  (less than the sum of the van der Waals radii of the O and H atoms\, whic
 h is 2.5 Å)\, there are no BCPs according to Bader’s analysis. Two poss
 ible ways of MeOH interaction with the B-Pyr acid are considered: formatio
 n of a cyclic complex (CC) and attack of the –C=O of the Pyr by MeOH. Th
 e CC is stabilised by two intermolecular HBs\, forming a six-membered ring
  (6MR) between the –COOH group atoms of the Pyr acid and the –OH group
  atoms of the MeOH molecule. The interaction energy is –66.48 kJ/mol. Th
 e CC have two tautomeric forms (causing asymmetry in the carbon skeleton)\
 , more twisted CCa and CCb\, which can interconvert through an activation 
 barrier of 42.40 kJ/mol. The transition state (TS) for the transition betw
 een CCa and CCb structural isomers is characterised by a flip-flop switchi
 ng of a hydrogen atom between adjacent acceptor centres (two O atoms of th
 e –COOH group and one O atom of the MeOH)\, forming a two-sided hydrogen
  trap. The configuration of CCb is thermodynamically more stable than CCa\
 , since its formation energy is lower by 4.43 kJ/mol.\n\nIn the second pat
 hway\, the MeOH molecule attacks the C=O bond of the Pyr\, forming a tetra
 hedral structure because the carbon atom orbitals in the –COOH group cha
 nge hybridisation from sp2 to sp3. This atom is bound to four substituents
 : a Pyr-based group (–C16H9)\, two –OH groups and a single methoxy gro
 up (–OCH3). The analysis of the atomic vibrations for the cyclic four-me
 mbered TS structure confirmed the presence of a single imaginary frequency
  at i1620.70 cm–1. The activation barrier is +169.01 kJ/mol\, and the ad
 sorption energy is +23.88 kJ/mol.\n \nBased on the obtained energetic para
 meters\, it was established that the bonding of the MeOH molecule preferen
 tially proceeds via the formation of 6MR CC structures\, as this pathway i
 s significantly more energetically favourable than direct attack on the C=
 O bond of the –COOH group.\n\nThis research was partially funded by the 
 National Research Foundation of Ukraine (grant 2023.03/0041).\n\nhttps://i
 ndico.bitp.kiev.ua/event/18/contributions/552/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/552/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Non-stationary longitudinal Josephson effect in bilayer systems wi
 th electron-hole pairing
DTSTART;VALUE=DATE-TIME:20260922T141000Z
DTEND;VALUE=DATE-TIME:20260922T141500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-522@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksandr Konstantynov (B.Verkin Institute for Low T
 emperature Physics and Engineering  of the National Academy of Sciences of
  Ukraine)\nThe non-stationary longitudinal Josephson effect in bilayer sys
 tems with pairing of spatially separated electrons and holes is investigat
 ed [1]. The tunneling current between two weakly coupled electron-hole con
 densates (right and left) is analyzed in the presence of an external volta
 ge applied along the layers. Two limiting regimes are considered: the high
 -density regime\, where pairing occurs in momentum space similarly to conv
 entional superconductors\, and the low-density regime corresponding to a B
 ose-Einstein condensate of spatially indirect excitons. Using the tunnelin
 g Hamiltonian approach\, expressions for the quasiparticle\, superconducti
 ng\, and interference contributions to the tunneling current are derived. 
 It is shown that in the high-density limit\, the quasiparticle and interfe
 rence currents vanish at zero temperature below a threshold voltage determ
 ined by the energy gap\, so that only the supercurrent remains. In contras
 t\, in the low-density regime\, the gapless spectrum of collective excitat
 ions leads to finite dissipative contributions even at zero temperature\, 
 resulting in damping of Josephson oscillations. For spatially separated tu
 nneling barriers with a distance exceeding the coherence length\, phase ju
 mps occur at each barrier\, resulting in voltage oscillations across the e
 lectron and hole barriers and a nonsinusoidal current-phase relation gover
 ned by the critical currents of the two barriers. Observation of the chara
 cteristic features of the longitudinal Josephson effect would provide dire
 ct evidence of superfluidity in the bilayer exciton condensate [2].\n\n[1]
  O. M. Konstantynov and S. I. Shevchenko\, Low Temp. Phys. **52**\, 1063 (
 2026). https://doi.org/10.1063/10.0044481\n[2] F. Pascucci\, A. R. Hamilto
 n\, M. V. Milošević\, and D. Neilson\, arXiv:2606.23303 (2026). https://
 doi.org/10.48550/arXiv.2606.23303\n\nhttps://indico.bitp.kiev.ua/event/18/
 contributions/522/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/522/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Comparative Analysis of Ion-Specific Effects on the Electrophysica
 l and Rheological Properties of DNA Aqueous Solutions with LiCl\, NaCl\, a
 nd KCls
DTSTART;VALUE=DATE-TIME:20260922T140500Z
DTEND;VALUE=DATE-TIME:20260922T141000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-531@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Mariia Sosnovska (Taras Shevchenko National Universi
 ty of Kyiv)\nDNA is a strong polyanionic polyelectrolyte with the properti
 es\, which are largely governed by interactions with charged ions (counter
 ions) in aqueous solution. Alkali metal cations differ substantially in io
 nic radius\, charge density\, and hydration enthalpy\, which in turn deter
 mine how strongly they bind to the phosphate backbone\, reorganize the sur
 rounding hydration shell\, and affect macroscopic transport and hydrodynam
 ic properties of the solution [1\,2].\nThis work presents a comparative an
 alysis of the electrical conductivity and viscosity of aqueous high-molecu
 lar-weight DNA solutions in the presence of LiCl\, NaCl\, and KCl across a
  common range of salt concentrations and temperatures. Rather than treatin
 g each system in isolation\, the ionic series Li⁺ → Na⁺ → K⁺ is 
 examined as a single trend\, allowing the relative contributions of cation
  size and hydration strength to charge transport and DNA conformational be
 havior to be disentangled. Comparison of the conductivity and viscosity re
 sponses reveals systematic\, ion-specific deviations that correlate with t
 he strength of cation–phosphate binding and the degree of ion dehydratio
 n upon association with DNA. The concentration- and temperature-dependence
  of these deviations further indicates how the balance between electrostat
 ic screening and hydration-shell restructuring shifts along the Li⁺–Na
 ⁺–K⁺ series.\nThese comparative trends provide a more direct route t
 o identifying the mechanisms underlying ion-specific effects in DNA–elec
 trolyte systems than analysis of individual salts alone\, and contribute t
 o a more general understanding of counterion selectivity in polyelectrolyt
 e solutions.\n[1]. Ross\, P. D.\, & Scruggs\, R. L. (1968). Viscosity stud
 y of DNA. II. The effect of simple salt concentration on the viscosity of 
 high molecular weight DNA and application of viscometry to the study of DN
 A isolated from T4 and T5 bacteriophage mutants. Biopolymers\, 6(8)\, 1005
 –1018. https://doi.org/10.1002/bip.1968.360060805\n[2]. Perepelytsya\, S
 .\, Piatnytskyi\, D.\, Bubon\, T.\, Cibotariu\, N.\, Laaksonen\, A.\, & Mo
 cci\, F. (2026). Ions as architects of DNA nanostructures: Mechanisms\, si
 mulations\, and technological frontiers. Small Structures\, 7\, e202500786
 . https://doi.org/10.1002/sstr.202500786\n\nhttps://indico.bitp.kiev.ua/ev
 ent/18/contributions/531/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/531/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Charge density oscillations around the DNA double helix
DTSTART;VALUE=DATE-TIME:20260922T140000Z
DTEND;VALUE=DATE-TIME:20260922T140500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-536@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksandr Cherniak (Bogolyubov Institute for Theoret
 ical Physics)\nThe DNA macromolecule has nanometer dimensions\, a double h
 elix structure consisting of chemically bonded atoms\, and a large negativ
 e charge. Being in an aqueous environment or inside cells\, the DNA macrom
 olecule interacts mainly through electrostatic forces\, hydrogen bonds\, h
 ydration and biochemical bonding\, including medium ions\, so the environm
 ent strongly influences DNA conformation\, stability and biological functi
 ons. Positively charged ions\, named counterions\, in the aqueous medium a
 round the DNA macromolecule\, play an important role as a screening cloud.
  Their motion is typically considered as strongly damped\, in particular d
 ue to medium viscosity and collisions\, and therefore\, counterion distrib
 ution is usually calculated in the electrostatic approximation. However\, 
 some studies demonstrate the possibility of high translational mobility of
  counterions in the screening cloud and their high-frequency movements ins
 ide the hydrated shells. Thus\, a counterion evolution around the DNA doub
 le helix remains an important problem.\nWe considered kinetic equations in
  the collisionless approximation and the DNA macromolecule approximation a
 s a charged cylinder with a weak and moderate electric field to describe t
 he counterion distribution evolution in the electric field of the DNA macr
 omolecule. Using such approximations\, the dispersion equations for counte
 rion oscillatory dynamics with an infinite number of oscillatory branches 
 are obtained. It is demonstrated that each of such branches is purely real
  if it is far from other branches\, while the intersection with other bran
 ches leads to instability. The upper bound of the instability coefficient 
 of the mode\, which appears at the branch intersection point\, is estimate
 d.\n\nThe author thanks to COSY COST Action CA21101\; National Research Fo
 undation of Ukraine (project № 2025.07/0355).\n\nhttps://indico.bitp.kie
 v.ua/event/18/contributions/536/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/536/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum-Chemical Study of the Interactions between DNA Phosphate G
 roups and Monovalent Ions
DTSTART;VALUE=DATE-TIME:20260922T135500Z
DTEND;VALUE=DATE-TIME:20260922T140000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-529@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Dmytro Piatnytskyi (Bogolyubov Institute for Theoret
 ical Physics)\nThe complexes of monovalent ions (Li$^+$\, Na$^+$\, K$^+$) 
 with DNA phosphate groups are considered in the present work. The complexe
 s are studied from the simplest to the more complicated ones. In addition\
 , chloride ions (Cl$^-$) and water molecules are introduced to make the co
 mplexes more realistic. Optimized geometries\, interaction energies\, and 
 vibrational spectra are calculated using density functional theory method 
 (DFT) within the framework of the Gaussian 03 software package.\nIt is sho
 wn that the lithium ion has a tetrahedral hydration shell. The calculated 
 interaction energies show that complexes containing Li$^+$ and two phospha
 te groups are energetically more stable than the corresponding complexes c
 ontaining sodium or potassium ions. IR and Raman spectra are obtained\, an
 d all the main vibrational modes are identified. Some of the calculated vi
 brational modes are in good agreement with experimental data.\nThe results
  of the present work may play a crucial role in understanding the possible
  condensation of DNA molecules in solution in the presence of Li$^+$ ions\
 , as suggested by some recent molecular dynamics calculations.\n\nAcknowle
 dgements: The study was supported by National Research Foundation of Ukrai
 ne (project No 2025.07/0355).\n\nhttps://indico.bitp.kiev.ua/event/18/cont
 ributions/529/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/529/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Electronic structure and stability of complexes Ag+ with nucleotid
 e base pairs
DTSTART;VALUE=DATE-TIME:20260922T135000Z
DTEND;VALUE=DATE-TIME:20260922T135500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-498@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yevhen Osokin (Bogolyubov Institute for Theoretical 
 Physics)\nMetallized DNA is of considerable interest due to its potential 
 application in molecular electronics. Therefore\, the fundamental properti
 es of this system are of paramount interest\, in particular those related 
 to electronic structure and dynamics of metallized base pairs. In this wor
 k\, two different structural motifs of Ag-DNA known from the experiment [1
 \,2] were investigated: one that preserves Watson-Crick base pairing with 
 Ag⁺ ions included in the base pairs (based on experiment [1])\, and the 
 other that breaks the base pairing (based on experiment [2]). The fundamen
 tal questions concerning their relative energetic stability and thermodyna
 mics of formation were considered. To answer these questions the detailed 
 quantum-chemical calculations were performed at the DFT level using the B3
 LYP functional in the Gaussian 03 software package. Ag+ ions were describe
 d by the Def2-TZVP basis set with effective core potential (ECP). Nucleoti
 de base atoms were described by the all-electron basis set 6-311++G(d\, p)
 . Solvation effects of the aqueous environment were taken into account usi
 ng the SMD model. Dispersion corrections were taken into account using met
 hod Grimme's of D3. This calculation method for the studied systems was ch
 osen based on the results of our previous work [3]. Several sets of system
 s were investigated\, both with and without Ag+\, including purine-Ag-puri
 ne\, pyrimidine-Ag-pyrimidine\, 7-deazapurine-Ag-pyrimidine\, and canonica
 l Watson-Crick base pairs. The highest thermodynamic stability was demonst
 rated by the neutral complex [7-deazaguanine(N1)-Ag+-cytosine(N3)]0\, whic
 h outperforms its canonical counterpart [guanine(N1)-Ag+-cytosine(N3)]0. A
 nalysis of the calculated IR and Raman vibrational spectra revealed pronou
 nced spectral changes that can be used to characterize the presence of Ag
 ⁺ ions in the DNA double helix. In particular\, vibrations associated wi
 th the motion of Ag⁺ ions were detected in the low-frequency region (\n\
 nhttps://indico.bitp.kiev.ua/event/18/contributions/498/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/498/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Machine learning to determine the fitting parameters of ferroelect
 ric-dielectric nanocomposites dielectric response
DTSTART;VALUE=DATE-TIME:20260922T134500Z
DTEND;VALUE=DATE-TIME:20260922T135000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-557@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksii Bereznykov (Institute of Physics\, NAS of Uk
 raine)\nOne of the problems of analyzing experimental electrophysical depe
 ndences is determining the parameters of the theoretical model that best r
 eproduces the form of measured dielectric response of ferroelectric-dielec
 tric nanocomposites. For complex nonlinear models\, such a problem may hav
 e several close solutions\, be sensitive to the initial approximation\, an
 d require significant computational costs. We investigated the possibility
  of using machine learning for automated determination of the parameters o
 f a physical model intended for forming an experimental state of the ferro
 electric-dielectric nanocomposites. The study of ferroelectric-dielectric 
 nanocomposites was conducted based on the Effective Medium Approximation (
 EMA) [1] and Heywang models [2]. For each model\, a set of curves was form
 ed when varying its physical parameters in given regions. Thus\, each curv
 e corresponds to a known set of parameters\, which allowed us to form a tr
 aining sample for the regression problem.\nTypically\, EMA considers a qua
 dratic equation for the effective permittivity of a binary mixture:\n$(1-
 μ)  \\frac{(ε_{eff}^*-ε_{b}^*)}{(1-n_a ) ε_{eff}^*+n_a  ε_b^*}+μ \\f
 rac{(ε_{eff}^*-ε_a^*)}{(1-n_a ) ε_{eff}^*+n_a  ε_a^*}=0$              
          (1)\nhere $ε_a^*\, ε_b^*$ are the relative complex permittiviti
 es of components "a" and "b" respectively\, $μ$ and $1-μ$ are the relati
 ve volume fractions of components "a" and "b" respectively\, and $n_a$ is 
 the depolarization field factor for the inclusion of type "a".\nFollowing 
 Heywang model\, the expected Arrhenius-type and/or the Mott-type temperatu
 re dependences (as well as a general stretched-exponential law) for the ef
 fective conductivity of the nanopowders could be modified by introduction 
 of the effective dielectric permittivity. Thus\, we use the following fitt
 ing function for effective conductivity:\n$σ_eff (T\,ω)=σ_A^0 (ω)exp[-
 (\\frac{E_A}{(k_B Tε_{eff}(T))}^λ ]$.                (2)\nHere $E_A$ is 
 an activation energy of the space charges in the cores/shells (A = C or S)
 . The positive fitting parameter $λ$ varies in the range $0\n\nhttps://in
 dico.bitp.kiev.ua/event/18/contributions/557/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/557/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Strain Engineering of Flexo-Phonons and Flexo-Ferrons in Thin Film
 s of Van der Waals Ferrielectrics
DTSTART;VALUE=DATE-TIME:20260922T134000Z
DTEND;VALUE=DATE-TIME:20260922T134500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-521@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Eugene Eliseev (Frantsevich Institute for Problems i
 n Materials Science\, National Academy of Sciences of Ukraine)\nIt was sho
 wn earlier that size effect of soft phonon dispersion is principally impor
 tant in nanosized ferroics [1]. Also\, the size and strain effects can det
 ermine the anomalous polarization reversal in strained thin films of van d
 er Waals ferrielectrics [2]. It has been shown recently that the influence
  of the flexoelectric coupling (shortly “flexocoupling”) on the fluctu
 ations of electric polarization and elastic strains can lead to the princi
 pal changes of the dispersion law of soft optical and acoustic phonons (sh
 ortly “flexophonons”) and ferrons (shortly “flexoferrons”) in a bu
 lk van der Waals ferrielectrics [3]. At that applied electric field influe
 nces strongly on the anisotropic dispersion of the flexocoupling induced p
 honons and ferrons in van der Waals ferrielectrics [4]. A strong coherent 
 ferrons and cavity acoustic phonons is predicted in the of van der Waals f
 errielectric $CuInP_2 S_6$ [5].\nUsing the Landau-Ginzburg-Devonshire appr
 oach\, in this work we reveal that the dispersion of flexophonons and flex
 oferrons is strongly dependent on the sign and magnitude of elastic strain
 s originated from the lattice constants mismatch in thin strained films of
  van der Waals ferrielectric $CuInP_2 S_6$. In particular\, the frequency 
 of acoustic flexophonons and flexoferrons tends to zero at nonzero wavevec
 tors $k>k_{cr}$\, where the critical value of the wavevector $k_{cr}$ is d
 etermined by the mismatch strain and flexocoupling strength. Zeroing of th
 e flexophonon frequency\, that appears with increase of tensile strains\, 
 indicates a possible emergence of a spatially modulated incommensurate pol
 ar phase induced by the flexo-strain effects. Analytical results\, derived
  in this work\, open the way for strain engineering of flexophonon and fle
 xoferron dispersion in thin films of van der Waals ferrielectrics.\nAcknow
 ledgements. The work is primary supported as part of the Computational Mat
 erials Sciences Program funded by the US Department of Energy\, Office of 
 Science\, Basic Energy Sciences\, under Award Number DE-SC0020145. The par
 t of A.N.M. and E.A.E. efforts are also supported by National Academy of S
 ciences of Ukraine (grants No. 5.8/26-П\, 1.4.B/222\, III-6-26). \nRefere
 nces\n1. A. N. Morozovska\, and E. A. Eliseev. Size effect of soft phonon 
 dispersion law in nanosized ferroics. Phys.Rev. B\, 99\, 115412 (2019)\; h
 ttps://link.aps.org/doi/10.1103/PhysRevB.99.115412\n2. A. N. Morozovska\, 
 E. A. Eliseev\, A. Ghosh\, M. E. Yelisieiev\, Y. M. Vysochanskii\, and S. 
 V. Kalinin. Anomalous Polarization Reversal in Strained Thin Films of CuIn
 P2S6\, Phys. Rev. B\, 108\, 054107 (2023)\; https://link.aps.org/doi/10.11
 03/PhysRevB.108.054107\n3. A. N. Morozovska\, E. A. Eliseev\, O. V. Berezn
 ikov\, M. Ye. Yelisieiev\, G.-D. Zhao\, Y. Zhu\, V. Gopalan\, L.-Q. Chen\,
  J.-M. Hu\, and Y. M. Vysochanskii\, Flexo-coupling induced phonons and fe
 rrons in Van der Waals ferroelectrics\, Physical Review B 112\, 014110 (20
 25)\; https://doi.org/10.1103/mr9v-khtj\n4. A. N. Morozovska\, E. A. Elise
 ev\, Y. Zhu\, Y. M. Vysochanskii\, V. Gopalan\, L.-Q. Chen\, and J.-M. Hu\
 , The Influence of Electric Field on the Anisotropic Dispersion of the Fle
 xocoupling Induced Phonons and Ferrons in Van der Waals Ferrielectrics. Jo
 urnal of Applied Physics\, 138\, 134101 (2025)\; https://doi.org/10.1063/5
 .0294057\n5. Y. Zhu\, Ji. Wu\, A. N. Morozovska\, E. A. Eliseev\, Y. M. Vy
 sochanskii\, V. Gopalan\, L.-Q. Chen\, X. Zhang\, W. Zhang\, J.-M. Hu. Str
 ong coupling between coherent ferrons and cavity acoustic phonons. Physica
 l Review Applied (2026)\; https://doi.org/10.1103/q9np-lk7y\n\nhttps://ind
 ico.bitp.kiev.ua/event/18/contributions/521/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/521/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Interacting Relativistic Bosons at Finite Temperatures:  Compariso
 n with Lattice QCD
DTSTART;VALUE=DATE-TIME:20260922T133500Z
DTEND;VALUE=DATE-TIME:20260922T134000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-564@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Denys Zhuravel (Bogolyubov Institute for Theoretical
  Physics of the National Academy of Sciences of Ukraine)\nWe study an inte
 racting relativistic system of charged bosons at finite temperature and fi
 xed isospin density within a thermodynamically consistent mean-field appro
 ach. Two forms of repulsive self-interaction\, $φ^4$ and $φ^6$\, are con
 sidered. The interactions lead to a density-dependent effective mass $M$ o
 f the bosonic quasiparticles and an associated excess-pressure contributio
 n. The thermodynamics is formulated in the Extended Canonical Ensemble\, o
 btained from the grand canonical description by a Legendre transformation 
 from the isospin chemical potential to the conserved isospin density. This
  formulation is particularly useful in the Bose-condensed phase\, where th
 e isospin chemical potential is constrained by the condensation condition\
 , $μI = M$\, and must be determined self-consistently.\nThe formalism is 
 applied to a pion-like system at finite isospin density and compared with 
 lattice-QCD results. We discuss the difference between the isospin chemica
 l-potential conventions used for pion and quark degrees of freedom and ado
 pt the convention in which the condensation threshold is $μI = mπ/2$. At
  $T = 122$ MeV\, the pressure\, isospin density\, energy density\, and tra
 ce anomaly are compared with lattice data. Both the $φ^4$ and $φ^6$ mode
 ls reproduce the main features of the lattice results\, with the φ6 inter
 action providing a better overall description. The results demonstrate tha
 t the Extended Canonical Ensemble provides a consistent framework for desc
 ribing interacting particle-antiparticle systems across the transition fro
 m the thermal to the Bose-condensed phase. \n\nThis work was funded by Nat
 ional Research Foundation of Ukraine grant 2025.07/0461.\n\nhttps://indico
 .bitp.kiev.ua/event/18/contributions/564/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/564/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theoretical analysis of astrophysical S-factors of nuclear reactio
 ns 7Be(n\,α)4He and 7Be(n\,p)7Li
DTSTART;VALUE=DATE-TIME:20260922T133000Z
DTEND;VALUE=DATE-TIME:20260922T133500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-545@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Victor Zhaba (Інститут теоретично
 ї фізики ім. М.М. Боголюбова НАН України)\n
 Theoretical analysis of astrophysical S-factors of nuclear reactions\n$^{7
 }$Be(n\,$\\alpha )^{4}$He and $^{7}$Be(n\,p)$^{7}$Li\n\nV.I. Zhaba\, V.S. 
 Vasilevsky\, Yu.A. Lashko\n\nBogolyubov Institute for Theoretical Physics\
 , National Academy of Sciences\nof Ukraine\n\nIn this report\, we study a 
 range of reactions induced by the interactions $^{7}$Li+p\, $^{7}$Be+n and
  $^{6}$Li+d. Special attention is paid to the low-energy region in the inp
 ut channels of reactions that take into account the dynamics of synthesis 
 and decay of $^{6}$Li\, $^{7}$Li and $^{7}$Be nuclei. This study is perfor
 med within a microscopic three-cluster model\, which allows us to involve 
 all binary channels of the $^{8}$Be decay. Besides\, this model takes into
  account polarizability of interacting nuclei (clusters) [1\, 2]. In Ref. 
 [3]\, this model was successfully applied to study the structure of the $^
 {8}$Be nucleus and the nature of high-energy resonance states of $^{8}$Be.
 \nWithin the framework of our model\, the astrophysical S-factors of the r
 eactions $^{7}$Be(n\,$\\alpha )^{4}$He\, $^{7}$Be(n\,p$_{0})^{7}$Li and $^
 {7}$Be(n\,p$_{1})^{7}$Li in the energy range E$_{cm}$=0-2 MeV were calcula
 ted. The dependence of the astrophysical S-factors on the form and intensi
 ty of the nucleon-nucleon interaction was investigated in detail. For the 
 astrophysical S-factor of $^{7}$Be(n\,$\\alpha)^{4}$He reaction\, the part
 ial 2$^{+}$ wave dominates over the entire energy range\, and is then enha
 nced by the 0$^{+}$ wave. The calculated S-factors for $^{7}$Be(n\,$\\alph
 a )^{4}$He reaction are further decomposed into contributions from reactio
 ns with $^{7}$Be in its ground and first excited states. For $^{7}$Be(3/2$
 ^{-}$)(n\,$\\alpha)^{4}$He reaction\, the 2$^{+}$ wave has a maximum that 
 is due to resonance. In our microscopic model\, this 2$^{+}$ resonance sta
 te appears at energy E$\\approx $1.27 MeV above $^{7}$Be+n decay threshold
 \, which is in good agreement with the experimental data obtained in [4].\
 nFor $^{7}$Be(n\,p$_{0})^{7}$Li reaction\, the 3$^{+}$ partial wave domina
 tes in the region of the maximum at Ecm=0.5 MeV\, while the 2$^{-}$ partia
 l wave determines the behavior at low and high energies. For $^{7}$Be(n\,p
 $_{1})^{7}$Li reaction\, the 1$^{-}$ partial wave dominates in the entire 
 energy range and together with the  $^{+}$\, 2$^{-}$\, 2$^{+}$ states prov
 ide the main contribution to the astrophysical S-factor. It was demonstrat
 ed that the cluster polarization has a large impact on value and energy de
 pendence of the S-factor for the $^{7}$Be(n\,p)$^{7}$Li reaction.\nThe cal
 culated astrophysical S-factors for the reactions $^{7}$Be(n\,$\\alpha)^{4
 }$He and $^{7}$Be(n\,p)$^{7}$Li are in good agreement with experimental da
 ta from leading laboratories. Our partial astrophysical S-factors for the 
 $^{7}$Be+n reactions are compared with calculations in the R-matrix theory
  and with data in the ENDF database.\n\n[1] Y.A. Lashko\, G.F. Filippov\, 
 V.S. Vasilevsky. Nucl. Phys. A 958\, 78 (2017).\n[2] V.S. Vasilevsky\, F. 
 Arickx\, J. Broeckhove\, T.P. Kovalenko. Nucl. Phys. A\n824\, 37 (2009).\n
 [3] V.I. Zhaba\, Yu.A. Lashko\, V.S. Vasilevsky. Phys. Rev. C 112 014328 (
 2025).\n[4] D.R. Tilley\, J.H. Kelley\, J.L. Godwin et al. Nucl. Phys. A 7
 45 155 (2004).\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/545/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/545/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hadronic and partonic composition of QCD matter across the crossov
 er
DTSTART;VALUE=DATE-TIME:20260922T132500Z
DTEND;VALUE=DATE-TIME:20260922T133000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-528@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Artemiy Lysenko (Bogolyubov Institute of Theoretical
  Physics)\nWe construct a simple equation of state of strongly interacting
  matter at zero chemical potentials that provides a unified description of
  lattice QCD thermodynamics in terms of hadronic and partonic degrees of f
 reedom. The hadronic phase is described by the quantum van der Waals hadro
 n resonance gas\, extended by excluded-volume repulsion between mesons\, w
 hile the quark-gluon plasma is modeled as an ideal gas of quarks and gluon
 s supplemented with a phenomenological interaction term proportional to $T
 ^3$. The two regimes are connected by a smooth crossover switching functio
 n. The three model parameters - the meson hard-core radius\, the strength 
 of the partonic interaction term\, and the switching temperature - are det
 ermined from a fit to lattice QCD results for the trace anomaly. The resul
 ting equation of state reproduces the lattice data on the pressure\, entro
 py density\, energy density\, and speed of sound in the temperature range 
 $T=100-500$ MeV. The fit yields a meson hard-core radius $r_M \\simeq 0.2$
  fm\, a partonic interaction scale $A \\simeq 600$ MeV\, and a switching t
 emperature $T_0 \\simeq 216$ MeV\, substantially exceeding both the pseudo
 critical temperature of the QCD chiral crossover and the chemical freeze-o
 ut temperature. This finding suggests that the transition from hadronic to
  partonic degrees of freedom is considerably more gradual than indicated b
 y the chiral pseudocritical temperature alone\, with hadronic states remai
 ning an important component of strongly interacting matter up to temperatu
 res of about $250$ MeV\, well above the QCD chiral crossover.\n\nhttps://i
 ndico.bitp.kiev.ua/event/18/contributions/528/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/528/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Longitudinal-momentum and Coulomb effects in inclusive deuteron br
 eakup on hydrogen and carbon
DTSTART;VALUE=DATE-TIME:20260922T132000Z
DTEND;VALUE=DATE-TIME:20260922T132500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-515@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yaroslav KRYVENKO-EMETOV (National Technical Univers
 ity of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute" & Institute for 
 Nuclear Research)\nYa. D. Krivenko-Emetov$^{1\,2\,3\,*}$ and B. I. Sydoren
 ko$^{2\,\\dagger}$\n\n$^{1}$National Technical University of Ukraine "Igor
  Sikorsky Kyiv Polytechnic Institute"\, Kyiv\, Ukraine\;$^{2}$Institute fo
 r Nuclear Research\, National Academy of Sciences of Ukraine\, Kyiv\, Ukra
 ine\;$^{3}$Taras Shevchenko National University of Kyiv\, Kyiv\, Ukraine$^
 {*}$y.kryvenko-emetov@kpi.ua\; $^{\\dagger}$former member of KINR NASU\n\n
 Inclusive zero-angle deuteron breakup probes the deuteron wave function an
 d the short-distance reaction mechanism. We present a unified Glauber--Sit
 enko multiple-diffraction description of the $H(d\,p)X$ and $^{12}C(d\,p)X
 $ spectra. The formulation develops the diffraction approach used in our w
 ork with A. P. Kobushkin [1] and continues the MSDT treatment of few-nucle
 on-cluster breakup\, including diffractive triton dissociation by incident
  protons [2]. In addition to the longitudinal transfer $Q_z$\, we explicit
 ly retain a nonzero transverse relative momentum of the final $pn$ pair in
  the antilaboratory system: $k_{\\perp}=p_{\\perp}-Q_{\\perp}/2\\ne0$\, wh
 ile $k_z=p_3^{*}$.\n\nFor $H(d\,p)X$\, retaining small $Q_z$ and transvers
 e relative momentum changes the height and position of the quasifree maxim
 um. Calculations with the multigaussian K2\, AV18\, and Nijm-I wave functi
 ons show that this refinement is essential for quantitative comparison wit
 h the spectrum and provides a controlled nucleonic baseline at large $|k_z
 |$ [3].\n\nFor $^{12}C(d\,p)X$\, the same kinematics is supplemented by th
 e proton--nucleus electromagnetic interaction\, Coulomb--nuclear interfere
 nce\, and the Coulomb correction to double $pn$ rescattering [4]. An analy
 tical Coulomb phase is obtained for a finite charge distribution\, with it
 s scale fixed by the measured $^{12}$C charge radius. To first order in th
 e Sommerfeld parameter\,\n\n$$F_{\\rm tot}=F_{\\rm str}+\\Delta F_{Cp}+\\D
 elta F_{Cpn}+O(\\eta^2)\,$$\n\nwhere $\\Delta F_{Cp}$ corrects the proton 
 line and $\\Delta F_{Cpn}$ corrects double $pn$ rescattering. Thus Coulomb
 --nuclear interference is retained\, and the two-dimensional rescattering 
 term is reduced to a one-dimensional radial integral\, extending earlier C
 oulomb treatments of $A(d\,p)X$ breakup [1].\n\n\n\n**Figure 1.** Results 
 for $^{12}C(d\,p)X$. Left panel: K2 wave function with $\\sigma_{pN}=390$ 
 mb\, $\\beta_p=1.22$ fm$^{-1}$\, $\\mu=0.25$ fm\, $a=1$\, $k_x=10^{-4}$ Ge
 V/$c$\, and $Q_z=-2.5\\times10^{-3}$ GeV/$c$. Right panel: Nijm-I wave fun
 ction with $\\sigma_{pN}=350$ mb\, $\\rho_{pN}=10^{-4}$\, $p_d=9.1$ GeV/$c
 $\, $\\beta_p=2.19$ fm\, $\\mu=10^{-6}$\, $a=\\alpha_L=1$\, $k_x=-0.26$ Ge
 V/$c$\, $k_y=0$\, and $Q_z=-2.5\\times10^{-3}$ GeV/$c$. The calculated gri
 d is $-0.10\\leq k_z\\leq0.25$ GeV/$c$ with $\\Delta k_z=0.0125$ GeV/$c$. 
 Therefore\, $k_\\perp=0.26$ GeV/$c$ and is nonzero in the antilaboratory s
 ystem. Red curve: strong MSDT\; green curve: MSDT with Coulomb\; blue poin
 ts: 2019 data [5].\n\n\nBoth the K2 and Nijm-I calculations show that Coul
 omb--nuclear interference increases the narrow quasifree peak and improves
  its normalization\, while becoming small at $0.3$--$0.5$ GeV/$c$. Thus\, 
 $Q_z$ and $k_\\perp$ govern the kinematic displacement and broadening\, wh
 ereas the finite-size Coulomb interaction mainly renormalizes the low-mome
 ntum peak. This provides a baseline for final-state interactions and for r
 elativistic refinements not included here: invariant flux and phase-space 
 Jacobians\; Lorentz boosts between the antilaboratory and final-$pn$ cente
 r-of-mass frames\; a covariant or light-front deuteron wave function with 
 spin rotations\; D-wave and nonnucleonic components.\n\nReferences\n\n[1] 
 A. P. Kobushkin and Ya. D. Krivenko-Emetov\, Ukr. J. Phys. 53\, 751 (2008)
 \, arXiv:0712.1151 [nucl-th].\n\n[2] V. K. Tartakovsky\, A. V. Fursaev\, a
 nd B. I. Sidorenko\, Phys. At. Nucl. 68\, 33--41 (2005)\, doi:10.1134/1.18
 58555.\n\n[3] Ya. D. Krivenko-Emetov and B. I. Sydorenko\, Nucl. Phys. At.
  Energy 27\, 16 (2026).\n\n[4] Ya. D. Krivenko-Emetov and B. I. Sydorenko\
 , arXiv:2607.17222 [nucl-th] (2026).\n\n[5] I. Sitnik\, EPJ Web Conf. 204\
 , 10011 (2019).\n\nKeywords: deuteron\; inclusive breakup\; Glauber--Siten
 ko theory\; longitudinal momentum transfer\; Coulomb--nuclear interference
 \; deuteron wave function\n\nhttps://indico.bitp.kiev.ua/event/18/contribu
 tions/515/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/515/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Geometric Singularities\, Moduli Stabilization\, and Gravitational
  Wave Signatures in String Compactifications
DTSTART;VALUE=DATE-TIME:20260922T131500Z
DTEND;VALUE=DATE-TIME:20260922T132000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-501@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Tetiana Obikhod (Institute for Nuclear Research NAS 
 of Ukraine)\nWe present a unified framework connecting Calabi--Yau geometr
 y\, singularity theory\, and early-universe cosmology within heterotic and
  Type IIB string compactifications. Starting from the Tian--Yau threefold 
 defined by its complete-intersection configuration matrix $P^3$ [3  0  1] 
  ${P}^3$ [0  3  1]\, we demonstrate how a free $\\mathbb{Z}_3$ quotient re
 duces the Euler characteristic to $\\chi=-6$\, yielding precisely three ch
 iral generations. By embedding a stable $SU(4)$ vector bundle with $c_1(V)
 =0$ and $c_2(V)=12 \\leq c_2(TX)=50$\, we satisfy the Green--Schwarz anoma
 ly cancellation condition while preserving $N=1$ supersymmetry and enablin
 g Wilson-line breaking of $E_6$ to the Standard Model gauge group.\n\nA ce
 ntral result is the identification of universal singularity structures gov
 erning vacuum transitions. Generic multi-field scalar potentials correspon
 d to non-simple singularities with Milnor number $\\mu=9$\, but near criti
 cal degeneracy loci the Hessian vanishes and the system universally reduce
 s to an $A_2$ cusp with $\\mu=2$ [1]. This reduction controls the dynamics
  of first-order phase transitions in the early universe. We derive the sto
 chastic gravitational-wave spectrum generated near these critical points\,
  showing that potential flattening enhances the signal amplitude as $\\Ome
 ga_{\\text{GW}} \\propto \\delta^{-3}$\, where $\\delta=1-\\hat{\\xi}/\\ha
 t{\\xi}_c$ measures the distance to criticality. The predicted peak freque
 ncies naturally lie in the milli-Hertz band\, and benchmark points satisfy
 ing strong first-order transition criteria yield $\\Omega_{\\text{GW}}h^2 
 \\sim 10^{-12}\\text{--}10^{-11}$\, placing them directly within the sensi
 tivity window of the LISA mission.\n\nWe systematically analyse the KKLT m
 oduli stabilisation mechanism [2] incorporating leading $\\alpha'^3$ corre
 ctions to the Kähler potential. The correction breaks the classical no-sc
 ale structure and generates three distinct vacuum regimes separated by a c
 ritical threshold $\\hat{\\xi}_c$. For $\\hat{\\xi}  \\hat{\\xi}_c$\, the 
 potential exhibits runaway behaviour characteristic of the Large Volume Sc
 enario or decompactification. The conifold transition mechanism [3]\, wher
 e massless black holes resolve geometric singularities via flop transition
 s\, provides a dynamical pathway connecting parent manifolds to the three-
 generation Tian--Yau/$\\mathbb{Z}_3$ vacuum. We quantify the tension betwe
 en shallow dS vacua near $\\hat{\\xi}_c$ and the de~Sitter swampland conje
 cture\, mapping the parameter space where controlled string constructions 
 remain consistent with quantum gravity constraints. Detailed derivations\,
  explicit benchmark tables\, and the full Hessian analysis are provided in
  [1]. Our results establish a direct observational bridge between compacti
 fication topology\, singularity-driven cosmology\, and gravitational-wave 
 detectors.\nKeywords: String compactification\, Tian--Yau threefold\, coni
 fold transitions\, singularity theory\, Milnor number\, KKLT mechanism\, $
 \\alpha'^3$ corrections\, gravitational waves\, LISA\, de~Sitter swampland
  conjecture.\n\n1.T. Obikhod\, "Supersymmetry\, Supergravity and Non--Pert
 urbative Dynamics of Gauge Theories\," arXiv:2604.19817v1 [hep-th] (2026).
 \n2.S. Kachru\, R. Kallosh\, A. Linde\, S.P. Trivedi\, "De Sitter vacua in
  string theory\," Phys. Rev. D68 (2003) 046005.\n3.A. Strominger\, "Massle
 ss black holes and conifolds in string theory\," Nucl. Phys. B451 (1995) 9
 6--108.\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/501/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/501/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Pragmatic View on the Measurement of Quanta
DTSTART;VALUE=DATE-TIME:20260922T131000Z
DTEND;VALUE=DATE-TIME:20260922T131500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-559@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Constantin Usenko (BITP)\nMeasuring a quantum\, as a
  purposeful activity of the Observer\, consists in obtaining and supplemen
 ting information about the quantum or simply checking the property of the 
 quantum for compliance with the expectation.\nHere\, a mathematically mean
 ingful representation of the Observer is proposed\, which is a set of devi
 ces capable of achieving the specified goal\, and the algorithm for the op
 eration of these devices.\n\nThe observer uses a personal mathematical mod
 el of the quantum and the measurement process. The completeness of the mat
 hematical tools depends on the purpose of the measurement.\nThe descriptio
 n of a quantum can be limited to the notion of a wave function and operato
 rs of observables\, or use the notion of state vectors and matrices of obs
 ervables\, and even be complicated to density matrices.\nSimilarly\, the s
 tatistical representation of probability\, when it is necessary to emphasi
 ze the difference between a random variable and its value\, can use the Ko
 lmogorov triad or even\, in the analysis of indirect measurements\, be com
 plicated to the Fr?chet representation of the random element.\n\nThe compo
 nents of the Observer are the Source\, the Measurer\, the Registar\, and t
 he Controller. The Source produces the desired state of the Quantum\, the 
 Measurer interacts with the Quantum\, the Registar performs the classical 
 measurement of the state of the Measurer\, and the Controller controls the
  process and records the result.\n\nA classical measurement of a quantum s
 ystem is considered to be a measurement of a degenerate observable that pr
 oduces information in an amount small compared to the von Neumann entropy 
 and is performed with an uncertainty that significantly exceeds the quantu
 m limit.	\n\nhe constructed mathematical model of the Observer determines 
 the location of the Heisenberg cut and sheds light on some paradoxes of qu
 antum theory\, such as the Wigner's friend paradox.\n\nhttps://indico.bitp
 .kiev.ua/event/18/contributions/559/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/559/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quanta Measurements are Indirect only
DTSTART;VALUE=DATE-TIME:20260922T130500Z
DTEND;VALUE=DATE-TIME:20260922T131000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-558@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Constantin Usenko (BITP)\nThe report presents  resul
 ts  of the Heisenberg Cut study in the theory of quantum measurement. The 
 solution to the problem was obtained thanks to perception of the impossibi
 lity of direct quanta measurement. An indirect test requires a deepening o
 f the random variable definition  via the Kolmogorov triad by the Frechet 
 representation of a random element.\n\nMeasurement in general is a purpose
 ful activity aimed at obtaining or at least deepening information about th
 e measured object\, therefore\, the theory of measurement contains\, along
  with a description of physical processes\, a description of the process o
 f converting the characteristics of the object into information.\n \nThe t
 erm "Measurement" as applied to quanta has three different interpretations
 . The simplest one means the act of interaction of a quantum with a measur
 ing device\, which ends in obtaining a certain value of the observable and
  a certain state of the quantum.\n Another interpretation is a series of t
 ests of a quantum in the same state using a single instrument. The uncerta
 inty in the measurement results of a non-degenerate observable is inversel
 y proportional to the square root of the number of tests.\nAnother interpr
 etation of the term "Measurement" is a set of such series with different i
 ncompatible devices\, such a measurement allows determining the state of a
  quantum if the number of incompatible devices is greater than the number 
 of independent degrees of freedom of the quantum.\n  \n\nThe specificity o
 f indirect measurement is the division of the measuring device into a mete
 r and a register. The meter directly interacts with the object of measurem
 ent\, the register messures  change  of the meter state to one that corres
 ponds to a certain measurement result. The Heisenberg cut is located betwe
 en the meter and the register.\n\nA sign of the classical nature of measur
 ement here is the incompleteness of the determination of the quantum state
  of the meter due to the use of degenerate observables\, when the relative
  decrease in the von Neumann entropy of the meter state in the process of 
 state recognition is small\, but the information obtained is sufficient to
  distinguish the results of the quantum measurement.\n\nhttps://indico.bit
 p.kiev.ua/event/18/contributions/558/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/558/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Longitudinal motion effects on transverse particle transport by ra
 ndom field
DTSTART;VALUE=DATE-TIME:20260922T130000Z
DTEND;VALUE=DATE-TIME:20260922T130500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-535@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksandr Cherniak (Bogolyubov Institute for Theoret
 ical Physics)\nTransport of a passive scalar in a given field is a common 
 problem in plasma systems\, the atmosphere\, ocean flows\, etc. It can be 
 formulated as a problem to recover the temporal evolution of a particle en
 semble in a given field based on known statistical characteristics of this
  field. An important peculiarity in such a system concerns the interplay o
 f two time scales\, namely the correlation time of the given field and the
  particle distribution function evolution time. When the correlation time 
 of the random field is much shorter than the particle distribution functio
 n evolution time\, the well-known Brownian motion approach is applicable t
 o such a system. When the situation is reversed\, new assumptions are need
 ed to build a correct statistical approach. The most vivid effects of thes
 e time scales interplay are obtained for two-dimensional systems\, yet the
  three-dimensional ones are also interesting from a practical point of vie
 w.\nFor the two-dimensional transport of the passive scalar\, we formulate
 d a unified statistical approach that takes into account finite and infini
 te correlation time and finite Larmor radius effects\, and that is able to
  correctly recover the transition from a sub-diffusive behavior for long c
 orrelation time to a diffusive one for short correlation time of a random 
 electric field. Such behavior of the asymptotic diffusion coefficient is i
 nseparable from particle trapping effects and the integral of motion that 
 is defined in two-dimensional systems. Although the three-dimensional syst
 ems lack such an integral of motion\, the effect of slow motion along the 
 third dimension is yet to be examined by our statistical approach.\nIn thi
 s work\, we consider a three-dimensional test particle motion in crossed r
 andom electric and constant magnetic fields. We present a statistical appr
 oach based on a two-dimensional one that takes into account particle motio
 n along a constant magnetic field. The calculations of transport coefficie
 nts obtained by this statistical approach are validated by direct numerica
 l simulation. The effects of finite Larmor radius\, finite correlation tim
 e and particle motion along the magnetic field on particle transport acros
 s the magnetic field are examined.\n\nhttps://indico.bitp.kiev.ua/event/18
 /contributions/535/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/535/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The friction in a system of relativistic charged particles
DTSTART;VALUE=DATE-TIME:20260922T125500Z
DTEND;VALUE=DATE-TIME:20260922T130000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-555@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Volodymyr Ognivenko (National Science Center Kharkiv
  Institute of Physics and Technology)\nA system consisting of a large numb
 er of relativistic charged particles is considered. An expression for the 
 friction coefficient in momentum space has been derived based on particle 
 dynamics under the action of the total force of binary interaction between
  charged particles. The derived formulas determine the particle friction c
 oefficients in momentum space\, both during the kinetic stage of the syste
 m's evolution at some preceding moment of time for the pre-Brownian partic
 le motion. General equations are used to derive the friction coefficient f
 or collisions between relativistic charged particles of different types. W
 e investigated radiation friction in a system of charged particles acting 
 as emitters. The motion of a stream of relativistic charged particles in a
 n external periodic field and the interaction of the particles via the ele
 ctromagnetic fields of their spontaneous radiation are considered. Express
 ions have been obtained for the longitudinal momentum-space friction coeff
 icient of particles for time intervals shorter than the particle motion ra
 ndomization time and for time intervals longer than the randomization time
 \, when the particle motion is completely random.\n\nhttps://indico.bitp.k
 iev.ua/event/18/contributions/555/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/555/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ising-Markov chains equivalence as an inverse problem of statistic
 al physics
DTSTART;VALUE=DATE-TIME:20260922T125000Z
DTEND;VALUE=DATE-TIME:20260922T125500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-505@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleg Usatenko (A.Ya. Usikov Institute for Radiophysi
 cs and Electronics Ukrainian Academy of Science)\nAn important problem in 
 the statistical description of big data random sequences is identifying ma
 croscopic characteristics that summarize the essential properties of the s
 ystem while ignoring microscopic details. These characteristics are analog
 ous to thermodynamic variables that describe the macroscopic state of a ph
 ysical system composed of many interacting degrees of freedom. Markov chai
 ns provide a natural starting point for such an analysis. Classical Nth-or
 der Markov chains allow one to describe correlations extending over long h
 istories but suffer from an exponential growth of parameters with increasi
 ng memory depth. Additive Nth-order Markov chains offer a principled reduc
 tion of this complexity by decomposing the conditional probability of the 
 next symbol into a superposition of contributions from different delay pos
 itions.\nIn Ref. [1]\, we established an exact correspondence of one- and 
 two-step-wise MC with one-dimensional Ising models with finite-range inter
 actions\, thereby introducing the macroscopic temperature to MC. We demons
 trated that information temperature could be defined through two independe
 nt approaches: (i) matching conditional probabilities\, and (ii) solving a
 n entropy-based inverse problem of statistical physics. In particular\, se
 e Ref. [2]\, it was understood that a complex system can be characterized 
 by temperature\, or in other words\, temperature is a fairly informative p
 arameter characterizing the complexity of a system.\nThe main result of th
 e work [3] is the establishment of a correspondence between an additive mu
 ltistep chain and a chain with a stepwise memory function. This correspond
 ence allows the introduction of the concept of information temperature not
  only for stepwise but also for general additive Nth-order Markov chains. 
 \nThe present work substantially extends that framework in several directi
 ons. First\, in addition to the two previous methods for introducing the i
 nformation temperature\, in this work\, we present a method based on joint
  probability. Second\, the equivalence between Markov chains and Gibbs-Isi
 ng representations is formulated within a constructive inverse statistical
  mechanics framework\, thereby making explicit the assumptions of positivi
 ty\, compatibility\, stationarity\, and finite memory. Third\, three compl
 ementary constructions of the information temperature are systematically c
 ompared and shown to be mutually consistent for the unbiased one-parameter
  step-wise Markov chain. Fourth\, the entropy-based definition is reformul
 ated as an inverse problem with an auxiliary energy scale\, clarifying its
  relation to the true Ising energy. Finally\, the analysis of the two-para
 meter inverse problem establishes the limits of this equivalence\, demonst
 rating that the coincidence of the three temperature constructions is a sp
 ecial property of the one-parameter model rather than a generic feature of
  finite-memory symbolic processes.\nThe primary objective for the future i
 s to understand the importance of introducing a macroscopic temperature pa
 rameter for characterizing Large Linguistic Models.\n\n[1] O. V. Usatenko\
 , S. S. Melnyk\, G. M. Pritula\,  and V. A. Yampol'skii\,   Phys. Rev. E  
 106\, 034127 (2022). \n[2]  O. V. Usatenko and G. M. Pritula\,  Chaos\, So
 litons and Fractals 202 (2026) 117452.\n[3] O. V. Usatenko\, G. M. Pritula
 \, and S. S. Melnyk\, Phys. Rev. E  114\, 014116 (2026).\n\nhttps://indico
 .bitp.kiev.ua/event/18/contributions/505/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/505/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sufficient and necessary conditions of entropy driven framework fo
 r hot unfolding of RNA thermometers
DTSTART;VALUE=DATE-TIME:20260922T124500Z
DTEND;VALUE=DATE-TIME:20260922T125000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-514@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksiy Kapitanchuk (Bogolyubov Institute for Theore
 tical Physics\, National Academy of Sciences of Ukraine)\nThe exchange of 
 matter and energy between an open system and its surroundings triggers the
 rmally activated spontaneous processes that drive entropy toward a maximum
 . Consequently\, thermal equilibration is fundamentally entropy-driven\, e
 stablishing a final equilibrium state whose population increases with temp
 erature.  In certain cases\, this behavior manifests as an entropy-driven 
 thermal extra-sensitivity. A prime biological example is found in specific
  bacterial mRNAs known as RNA thermometers\, which exhibit an extraordinar
 ily sharp\, temperature-dependent regulation of their translation initiati
 on rate. This regulatory capacity stems from conformational unfolding near
  their ribosome-binding sites. However\, a rigorous thermodynamic derivati
 on of the master equation governing this entropy-driven unfolding has rema
 ined elusive.\nThis report establishes the sufficient and necessary condit
 ions of an entropy-driven framework to model the hot unfolding of RNA ther
 mometers withing a two-configuration approximation. By restricting the sys
 tem to transitions between two primary states (folded and unfolded) a cons
 istent equation for the thermodynamic probability of the entropy-driven un
 folding process is derived. The probability of the unfolded state is deter
 mined and its temperature dependence is mapped. This formulation reveals t
 hat the fundamental necessary condition for an entropy-driven unfolding pr
 ocess is that the entropy of the initial folded state exceeds the entropy 
 of the initial unfolded one\, both calibrated at an initial temperature. W
 ith rising the temperature\, this condition breaks making the unfolding pr
 ocess to be steeply temperature-dependent in a power-like form such that t
 he temperature exponent becomes equal the excess heat capacity at constant
  pressure\, scaled in units of the gas constant. Furthermore\, it is demon
 strated that a high heat capacity increment is driven by an increased numb
 er of degrees of freedom and a growing degeneracy of the unfolded state. T
 he sufficient condition is constituted by explaining the thermal extra-sen
 sitivity of the biomolecules in the framework of entropy-driven scenario\,
  in which the change of enthalpy is considered as minor process\, whereas 
 that of entropy change is regarded prevalent and increasing with temperatu
 re. Finally\, the derived approach shows excellent agreement with existing
  experimental data of melting curves on mRNA unfolding transitions\, thus 
 providing a robust thermodynamic background for RNA thermometry.\n\nThe au
 thors acknowledge the support by the NAS of Ukraine through the project No
 .01261U001252.\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/514/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/514/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Axion-Like Dark Matter Feedback from Subgalactic Baryon Redistribu
 tion
DTSTART;VALUE=DATE-TIME:20260922T124000Z
DTEND;VALUE=DATE-TIME:20260922T124500Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-526@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Andriy Nazarenko (Bogolyubov Institute for Theoretic
 al Physics of NAS of Ukraine)\nWe investigate the hydrodynamic and quantum
  evolution of dark matter (DM) modeled as a Bose–Einstein condensate (BE
 C) with axion-like self-interaction within dwarf galaxies. The periodic na
 ture of the interaction induces a multiphase halo structure with alternati
 ng stability zones\, where low-density spatial tails undergo spinodal deco
 mposition and fragment into clump- and foam-like structures [1]. While a m
 assive solitonic core (~12% of total mass) provides local gravitational sh
 ielding\, subgalactic structures remain highly susceptible to perturbation
 s driven by baryonic redistribution. Focusing on the core boundary of NGC 
 2366\, we show that baryonic variations induce a DM gravitational trap tha
 t enables long-term gas cooling and collapse\, predicting the formation of
  a $10^6$ M_ʘ star cluster over 50 Myr. Conversely\, linearized simulatio
 ns of localized feedback scenarios (shell dynamics and dynamical friction)
  reveal highly suppressed DM winds (≲several m/s)\, challenging direct o
 bservational detection. To address the long-term cumulative impact of mult
 iple baryonic events\, we develop a quantum excitation framework. We demon
 strate that the lowest long-wavelength radial mode acts as a false vacuum 
 state\, undergoing non-viscous quantum relaxation with a characteristic de
 cay lifetime of 68 Myr [2]. This mechanism drives a universal exponential 
 damping of the system's evolution\, while a nonlinear three-mode parametri
 c energy exchange governs the subsequent redistribution of stable quasipar
 ticle excitations.\n\n[1]	A. Nazarenko\, Macroscopic states in Bose–Eins
 tein condensate dark matter model with axionlike interaction\, Eur. Phys. 
 J. C 85 (2025) 1171.\n[2]	A. Nazarenko\, Axionlike dark-matter winds drive
 n by galactic baryon redistribution\, arXiv:2603.22234 [astro-ph.GA].\n\nh
 ttps://indico.bitp.kiev.ua/event/18/contributions/526/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/526/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Liquid theory of spherical and unitary designs
DTSTART;VALUE=DATE-TIME:20260922T113000Z
DTEND;VALUE=DATE-TIME:20260922T120000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-499@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Jorge Kurchan (Ècole Normale Supèrieure de Paris)\
 n"Designs" are sets of points\, for example on a sphere\, that have the pr
 operty that averages of polynomials over the set coincide with averages ov
 er the whole sphere. Similarly for the unitary group.\nOne can  treat thes
 e points as interacting particles\, and use liquid theory to study the pro
 blem. I will present the problem as seen from a physicist's point of view.
 \n\nhttps://indico.bitp.kiev.ua/event/18/contributions/499/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/499/
END:VEVENT
BEGIN:VEVENT
SUMMARY:M.M. Bogolyubov and theoretical physics in Kharkiv
DTSTART;VALUE=DATE-TIME:20260923T113000Z
DTEND;VALUE=DATE-TIME:20260923T120000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-563@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yuriy Slyusarenko (O.I. Akhiezer Institute for Theor
 etical Physics\, NSC KIPT and V.N. Karazin Kharkiv National University)\nT
 he "genealogy" of theoretical physics in Kharkiv from the beginning of the
  1930s to the present is presented. The connection is traced both at the l
 evel of research topics and at the level of interpersonal relations betwee
 n representatives of the Kyiv school of theoretical physics\, founded by M
 .M. Bogolyubov\, and the Kharkiv school of theoretical physics\, founded b
 y L.D. Landau and O.I. Akhiezer. The main attention is paid to the interse
 ction of research topics in statistical physics of both schools\, in parti
 cular\, to the methods of statistical physics in the theory of irreversibl
 e processes.\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/563/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/563/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Modern trends in plasma wakefield acceleration
DTSTART;VALUE=DATE-TIME:20260923T150000Z
DTEND;VALUE=DATE-TIME:20260923T152000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-562@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Vasyl Maslov ()\nHigh-efficiency acceleration of cha
 rged particle beams in the plasma wakefield accelerator was studied experi
 mentally and by numerical simulation. The most impressive experimental res
 ults [1] until now in electron accelerating by a wakefield\, excited in a 
 plasma\, have been achieved using capillary-generated plasma. Plasma-wakef
 ield acceleration provides high accelerating gradients [1\,2]\, promises c
 ompact accelerators of high-brightness and high-energy electron beams. App
 lications of plasma-wakefield accelerators\, in particular\, particle coll
 iders and free-electron lasers demand low energy spread beams\, their smal
 l emittance\, high current of accelerated bunches\, large transformer rati
 o and high-efficiency operation. Achievement of these requires plateau for
 mation on both the accelerating field for witness-bunch and the decelerati
 ng fields for driver-bunch. As it is known plateau formation is possible b
 y controlled beam loading with careful shaping current profile and beam ch
 arge selection. We will demonstrate by numerical simulation by PIC code an
 d analytically such optimal beam loading in plasma wakefield accelerators.
  Problems of acceleration of positron bunches in plasma\, focusing and sta
 ble transport of electron and positron bunches in plasma are important. In
  the blowout regime the hose instability can appear. Earlier investigation
 s [3\,4] show that the instability is essentially suppressed if the focusi
 ng force is inhomogeneous along the bubble\, and radial inhomogeneity can 
 be additional effect. The problem of the instability can be solved in weak
 ly nonlinear regime. In weakly nonlinear regime throughout the areas of th
 e driver and witness bunches the focusing force is inhomogeneous. Radial i
 nhomogeneity of residual plasma electron distribution also leads to bunch 
 stabilization. We will present results of analytical investigation of hose
  instability suppression in plasma wakefield accelerator driven by electro
 n bunch in the weakly nonlinear and blowout regimes. \nThe resonant sequen
 ce of electron bunches can be unstable due to the destruction of the bunch
 es. In this report we show by numerical simulation and analytically the po
 ssible way of suppressing this instability by shaping of the bunches. \nWe
  will present in the paper results on: \n- wakefield passive plasma lenses
  (due to loading effect) for identical focusing of short or long homogeneo
 us electron or positron bunch or Gaussian bunch depending on its length\, 
 charge for stable electron or positron beam propagation in a plasma column
 \; \n- optimal beam loading for the self-consistent distributions of a dec
 elerating wakefield of plateau type for a driver-bunch and an accelerating
  wakefield of plateau type for a witness-bunch during all time of accelera
 tion\; \n- control of optimal field shape (by loading effect)\, accelerati
 ng electron or positron bunch in plasma wakefield\; \n- obtaining long ele
 ctron witness-bunch of good quality (due to loading effect) in plasma wake
 field accelerator at high transformer ratio\, \n- damping hose instability
  in plasma wakefield accelerator\;\n- double bunches and twin-bunch in con
 ditions and places of best bunch stability with plateaus on wakefield in P
 WFA.\nReferences\n1.W.P. Leemans et al. Phys. Rev. Lett. 113 (2014) 245002
 . \n2.V.I.Maslov et al. Problems of Atomic Science and Technology. 6\, 52 
 (2021). \n3.A.Martinez de la Ossa et al. Phys. Rev. Let. 121\, 064803 (201
 8). \n4.G.Loisch et al. J.Phys.: Conf. Ser. 1596\, 012003 (2020).\n\nhttps
 ://indico.bitp.kiev.ua/event/18/contributions/562/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/562/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Cosmology Probes for Fundamental Physics
DTSTART;VALUE=DATE-TIME:20260923T120000Z
DTEND;VALUE=DATE-TIME:20260923T123000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-561@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Carlo Baccigalupi (International School for Advanced
  Studies)\nTBA\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/561/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/561/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Macroscopic rotational constraints on the neutron-star radius
DTSTART;VALUE=DATE-TIME:20260923T081000Z
DTEND;VALUE=DATE-TIME:20260923T083000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-560@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Alexander Magner (IInstitute for Nuclear Research of
  the National Academy of Sciences)\nThe macroscopic model for neutron star
 s (NSs) as a cold perfect fluid in equilibrium within the Tolman-Oppenhiem
 er-Volkoff (TOV) theory is extended to a small rotational angular momentum
  I around the symmetry axis. The deformed NS surface was taken into accoun
 t in the leptodermic approximation $a/R R$) and Hogan inner ($r \n\nhttps:
 //indico.bitp.kiev.ua/event/18/contributions/560/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/560/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum-Mechanical Analysis of Electron Transport in a Cylindrical
  Crossed-Field Configuration with a Periodic Boundary Potential
DTSTART;VALUE=DATE-TIME:20260924T142000Z
DTEND;VALUE=DATE-TIME:20260924T144000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-554@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Dmytro Kadygrob (O. Ya. Usikov Institute for Radio P
 hysics and Electronics of the National Academy of Sciences of Ukraine)\nTh
 is work presents a fully quantum-mechanical theoretical framework for desc
 ribing electron dynamics and collective phenomena in a cylindrical crossed
 -field configuration subject to a spatially periodic boundary potential. T
 he electron cloud is considered in orthogonal radial electric and axial ma
 gnetic fields. By solving the Schrödinger equation with the corresponding
  gauge potentials and an effective radial potential in cylindrical coordin
 ates\, we obtain the quantized energy spectrum and spatial structure of th
 e electron states.\n    In the unperturbed state\, the quantum-mechanical 
 analysis shows that the radial current vanishes. Electron transport toward
  the boundary is therefore described as a quantum process associated with 
 transitions between discrete angular-momentum states induced by a spatiall
 y inhomogeneous high-frequency field. The periodic boundary potential coup
 les states with different angular momenta and provides a mechanism for pha
 se locking and coherent energy transfer between the electron cloud and the
  electromagnetic field.\n    A key result of the work is the identificatio
 n of a mathematical correspondence between the formation of azimuthal spac
 e-charge structures\, commonly referred to as spokes\, and the collective 
 phenomena described by the Landau theory of second-order phase transitions
  and the Ginzburg–Landau theory. The emergence of rotating electron bunc
 hes is interpreted as a spontaneous symmetry-breaking process\, while the 
 spokes are described as stable\, spatially coherent structures of a comple
 x order parameter.\n    The proposed framework establishes a connection be
 tween microscopic quantum electron dynamics and macroscopic order-paramete
 r theory\, providing a unified description of electron transport\, collect
 ive self-organization\, phase coherence\, and nonlinear evolution of azimu
 thal space-charge structures in cylindrical crossed-field configurations.\
 n\nhttps://indico.bitp.kiev.ua/event/18/contributions/554/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/554/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The mobility of a mono-vacancy in 2D graphene studied with molecul
 ar dynamics
DTSTART;VALUE=DATE-TIME:20260923T101000Z
DTEND;VALUE=DATE-TIME:20260923T103000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-551@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Ari Paavo Seitsonen (Département de Chimie\, École
  Normale Supérieure)\nThe graphene has become a widely investigated mater
 ial since its controlled isolation and identification 20 years ago\, and i
 t started the boom of the two dimensional materials. The electronic\, mech
 anical and other properties of graphene are affected by the native defects
  in it. Here we study the simple one\, a mono-vacancy. A question about it
 s mobility has been raised by the community of experimental groups perform
 ing imaging of graphene witht the Scanning Tunnelling Electron Microscopy 
 (STEM)\, because they see \n\nIn order to give an answer to this question 
 we performed molecular dynamics simulations of the graphene with a mono-va
 cancy at different temperatures\, and from the rate of diffusion we estima
 te the hopping rate of the vacancy and thus the time of temporary stabilit
 y at a given site. The potential we used is a machine learning interaction
  potential fitted to data from similar simulations with the density functi
 onal theory. The fitted potential allows us to run much longer simulations
  at a modest computing cost\, with a system that is also larger than feasi
 ble with electronic structure calculations.\n\nIn this preliminary report 
 of our results we compare our results with the earlier ones given in the l
 iterature.\n\n\n\nThe spin electron density on the atoms around the vacanc
 y in graphene from the DFT\n\nhttps://indico.bitp.kiev.ua/event/18/contrib
 utions/551/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/551/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Coherent effects in atomic K-shell ionization and characteristic X
 -ray emission by ultrashort high-energy electron bunches
DTSTART;VALUE=DATE-TIME:20260923T125000Z
DTEND;VALUE=DATE-TIME:20260923T131000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-550@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Vsevolod Skorobohatov ()\nThe coherent effects prese
 nt in atomic K-shell ionization and the subsequent emission of characteris
 tic X-ray radiation (CXR) induced by ultrashort relativistic electron bunc
 hes are investigated [1]. The approach distinguishing close and distant co
 llisions was applied to calculate the K-shell ionization cross section. Th
 e cross section associated with close collisions is independent on the num
 ber of electrons in the bunch and can be calculated using the approximatio
 n of hard binary electron-electron collisions. Meanwhile\, the cross secti
 on associated with distant collisions is affected by coherent effects and 
 was of primary interest. It was calculated based on the Weizsäcker-Willia
 ms method of equivalent photons.\n    \nIt was shown that the interference
  between the proper electromagnetic fields of single electrons can lead to
  a significant coherent enhancement of the ionization cross section in thi
 n light-element targets\, particularly beryllium and carbon. In particular
 \, the case of a microbunched beam was investigated using a periodically m
 odulated distribution of the bunch number of particles in longitudinal dir
 ection. According to calculations made for parameters of bunches achievabl
 e at modern X-ray free electron lasers\, a strong resonant amplification o
 f the cross section occurs. This leads to an enhancement of the ionization
  cross section by several orders of magnitude for a wide range of microbun
 ching periods.\n\nMoreover\, the analysis was extended to targets of arbit
 rary thickness to study the evolution of the K-shell ionization cross sect
 ion caused by the medium polarization (density effect) along the beam prop
 agation path. It was found that the cross section decreases with increasin
 g the depth of the beam penetration into the target\, reaching a plateau w
 hen the penetration depth significantly exceeds the absorption length of a
  photon with an energy equal to the K-shell ionization threshold. Furtherm
 ore\, it was shown that the main contribution to the CXR photons emitted f
 rom the target comes from a thin near-surface layer\, whose thickness can 
 be much smaller than the CXR attenuation length\, unlike in the case of a 
 single electron interacting with the target. The reasons for this are disc
 ussed.\n\nThe obtained results and the considered coherent effects could b
 e applied to the development of new techniques for diagnostics of paramete
 rs of subfemtosecond electron bunches.\n\nhttps://indico.bitp.kiev.ua/even
 t/18/contributions/550/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/550/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The uses of the SO(5)/SO(2) Stiefel sigma model for the unified Zh
 ang's model
DTSTART;VALUE=DATE-TIME:20260924T075000Z
DTEND;VALUE=DATE-TIME:20260924T081000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-549@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yuliia Lunha (Bogolubov Institute for Theoretical Ph
 ysics)\nWe investigate the critical behavior and phase structure of nonlin
 ear sigma models on real Stiefel manifolds SO(N)/SO(N-k)\, with particular
  focus on the SO(5)/SO(2) model and its relation to the $SO(5)$-based Zhan
 g model of competing antiferromagnetic and superconducting orders. The Sti
 efel model is characterized by two effective interaction coupling constant
 s\, which give rise to a tetracritical regime implying\, in particular\, t
 he appearance of the phase with coexistence of antiferromagnetic and super
 conducting orders. We analyze the scaling behavior and properties of the f
 our phases using both Hamiltonian and Lagrangian formulations. In particul
 ar\, we determine quasiparticle masses and apply these to characterize the
  symmetry breaking in different phases\, including the mixed phase where t
 he two orders coexist. As one of our main results we present the determina
 tion of "transverse" critical exponents for the tetracritical point. These
  exponents complement the previously obtained critical exponents in the (T
 )-direction and provide a more complete characterization of the associated
  universality classes. Note that the transverse critical exponents are obt
 ained for the general class of Stiefel models SO(N)/SO(N-k). We further ex
 amine the electron–hole asymmetry\, which is not intrinsically incorpora
 ted in the Zhang model but emerges naturally in the Stiefel model framewor
 k. For the SO(5)/SO(2) model\, the resulting carrier charge has the physic
 ally relevant sign\, in contrast to the SO(5)/SO(3) Stiefel model which\, 
 in addition\, does not exhibit tetracritical behavior. The obtained result
 s establish an important connection between the critical structure (and ph
 ases) of Stiefel sigma models and the phenomenology of competing antiferro
 magnetic and superconducting orders.\n\nhttps://indico.bitp.kiev.ua/event/
 18/contributions/549/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/549/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Associative approach in soft matter theory
DTSTART;VALUE=DATE-TIME:20260922T095000Z
DTEND;VALUE=DATE-TIME:20260922T102000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-548@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Myroslav Holovko (Yukhnovskii Institute for Condense
 d Matter Physics of NAS of Ukraine)\nWe analyse the possibility of the app
 lication of the statistical-mechanical approaches developed in the modern 
 theory of associative fluids for the description of associative phenomena 
 on different properties in soft matter theory [1]. In developed theoretica
 l formalism\, the potentials of intermolecular interactions are split into
  three parts. One of them is the short-range repulsive part responsible fo
 r excluded volume effects by molecules. The second one is the short-range 
 strongly attractive part responsible for different clusterization effects\
 , including self-assembly phenomena. The third part is long-range and resp
 onsible for the screening and renormalization phenomena. The specificity o
 f the developed approach are connected with the application of the activit
 y diagram expansions for the description of the short-range attractive par
 t of interactions and the density diagram expansions for the description o
 f the last two parts of interactions. Classification and reduction of the 
 obtained diagrams in such expansions leads to the multidensity formalism\,
  whose specificity strongly depends on types of described clusterization p
 henomena. Special attention is focused on the application of the associati
 ve approach in the theory of ionic solutions. The analytical solution of t
 he associative mean spherical approximation (AMSA) and the modified versio
 n of the mean spherical approximation - the mass action law (MSA-MAL) appr
 oach are used to revise the concept of ion association in the theory of el
 ectrolyte solutions. It is shown that AMSA theory is more preferable for t
 he description of thermodynamical properties while the modified version of
  the MSA-MAL theory is more useful for the description electrical properti
 es [2]. The proposed theory is applied to explain the anomalous properties
  of the electrical double layer in a low temperature region and for the tr
 eatment of the effect of electrolyte on the rate of intermolecular electro
 n transfer. We applied the developed approach for the description of solub
 ilization of biological molecules in reverse micellar systems and the stud
 y of biomolecules' influence on the properties of considered systems. As a
 n example\, we consider solubilization of cytochrome-c in water in oil rev
 erse micellar system [3] and the solubilization of RNA in water in reverse
  wormlike micellar systems with lipid covering. The associative approach a
 lso gives the possibility to construct the macromolecular\nsystems from ch
 emical functional groups.\n\nhttps://indico.bitp.kiev.ua/event/18/contribu
 tions/548/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/548/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Low-Rank Split-Operator Propagation for Structured Open Quantum Sy
 stems
DTSTART;VALUE=DATE-TIME:20260924T112000Z
DTEND;VALUE=DATE-TIME:20260924T114000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-547@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Roman Ovsiannikov (NSC «Kharkov Institute of Physic
 s and Technology»)\nDirect numerical simulation of open quantum systems i
 s limited by the quadratic memory cost of storing the density matrix. We p
 resent a deterministic low-rank propagation method for time-local Markovia
 n dynamics. The method applies to Hamiltonians composed of a time-dependen
 t diagonal part and terms that become tridiagonal after suitable permutati
 ons of the basis\, as well as to collapse operators with diagonal or narro
 w-banded representations. The density matrix is represented by a low-rank 
 ensemble of state vectors. Coherent evolution is advanced using a symmetri
 c Suzuki–Trotter decomposition: diagonal factors are applied exactly\, w
 hile tridiagonal factors are evaluated using Cayley transforms that requir
 e only solving tridiagonal linear systems. Dissipation is incorporated thr
 ough infinitesimal Kraus branches\, after which the enlarged ensemble is c
 ompressed to a prescribed rank using a small Gram matrix. For a fixed reta
 ined rank and number of collapse channels\, the memory requirement and the
  dominant computational operations scale linearly with the Hilbert-space d
 imension.\n\nThe method is benchmarked on a driven finite-spin model of an
  NV-center ensemble coupled to a microwave cavity. The interaction terms b
 ecome tridiagonal in different basis orderings\, while the cavity and coll
 ective-spin collapse operators retain a banded structure. Comparison with 
 full-density-matrix simulations in QuTiP shows close agreement for the cav
 ity quadrature variance in the tested regime\, while the integrated errors
  of the monitored observables decrease systematically as the retained rank
  is increased from 2 to 16. Pure-propagation timing benchmarks exhibit nea
 r-linear scaling\, with fitted exponents between 1.09 and 1.23. The method
  is therefore most effective when the density matrix remains approximately
  low rank\; strongly mixed states and continuously pumped lasing regimes m
 ay require larger ranks and reduce the computational advantage.\n\nhttps:/
 /indico.bitp.kiev.ua/event/18/contributions/547/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/547/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ensemble-Averaged Axion–Photon Conversion in Turbulent Galaxy Cl
 usters
DTSTART;VALUE=DATE-TIME:20260923T123000Z
DTEND;VALUE=DATE-TIME:20260923T125000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-544@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksandr Khasai (Bogolyubov Institute for Theoretic
 al Physics of the National Academy of Sciences of Ukraine)\nAxion-like par
 ticles (ALPs) coupled to photons can modify electromagnetic spectra throug
 h conversion in astrophysical magnetic fields. In galaxy clusters\, turbul
 ence makes this effect stochastic and strongly dependent on the magnetic-f
 ield realisation for individual sightlines. Recent work showed that averag
 ing over ensembles of background active galactic nuclei transforms these f
 luctuations into a smooth\, universal absorption-like feature\, enhancing 
 the sensitivity of cluster ALP searches [1\,2]. We develop an analytic des
 cription of this ensemble-averaged signal and establish the connection bet
 ween physical turbulence spectra and the domain models commonly used in nu
 merical simulations.\n\nTurbulent fields are often represented by uniform 
 domains with sizes distributed as $p(\\Delta)\\propto\\Delta^{\\beta-1}$\,
  while a physical turbulent field is characterised by $\\langle|B_k|^2\\ra
 ngle\\propto k^{-a-2}$\, corresponding to an energy spectrum $\\propto k^{
 -a}$ and $a=5/3$ for Kolmogorov turbulence. In the perturbative regime\, t
 he ensemble-averaged conversion probability is determined by the one-dimen
 sional power spectrum of the transverse field along the line of sight [3].
  Matching the exact domain-model correlator to the turbulent structure fun
 ction gives $\\beta = a - 2$ for $1  0$ universally produces an effective 
 $k^{-2}$ spectrum because of the discontinuities at domain boundaries\, wh
 ile spectra with $a > 2$ cannot be reproduced by this class of models.\n\n
 Using this correspondence\, we derive the ensemble-averaged conversion pro
 bability in closed form for arbitrary $\\Delta_{\\min}/\\Delta_{\\max}$ an
 d obtain a simple two-power-law approximation. The resulting feature start
 s at $\\omega_c\\sim m_a^2\\Delta_{\\max}/2$\, rises approximately as $\\o
 mega^a$\, and saturates at high energies with an amplitude controlled by t
 he magnetic-field correlation length. Thus\, the inertial-range turbulence
  fixes the spectral shape\, while the high-energy plateau retains an $\\ma
 thcal{O}(1)$ sensitivity to the modelling of the largest field scales.\n\n
 Our results provide an analytic dictionary between turbulent spectra and d
 omain-size prescriptions\, removing an ad hoc parameter from cluster ALP s
 imulations. They also provide an analytic alternative to Monte-Carlo avera
 ging over magnetic-field realisations\, offering a practical framework for
  interpreting existing ensemble searches and constructing efficient templa
 tes for future observations [1\,2].\n\nReferences:\n[1]D. Malyshev\, L. Za
 dorozhna\, Yu. Bidasyuk\, A. Santangelo\, and O. Ruchayskiy. Constraints o
 n axion-like particles from active galactic nuclei seen through galaxy clu
 sters. Nature Astronomy\, 9:1387–1395\, September 2025. doi:10.1038/s415
 50-025-02621-8\n[2]D. Malyshev\, L. Zadorozhna\, Yu. Bidasyuk\, A. Santang
 elo\, and O. Ruchayskiy. AGN spectral variability across activity states a
 nd searches for axion-like particles. arXiv e-prints\, art. arXiv:2509.223
 44\, September 2025. doi:10.48550/arXiv.2509.22344.\n[3]M. C. D. Marsh\, J
 . H. Matthews\, C. Reynolds\, and P. Carenza. Fourier formalism for relati
 vistic axion-photon conversion with astrophysical applications. Phys. Rev.
  D\, 105(1):016013\, 2022. doi:10.1103/PhysRevD.105.016013\n[4]J. P. Conlo
 n\, F. Day\, N. Jennings\, S. Krippendorf\, and M. Rummel. Constraints on 
 Axion-Like Particles from Non-Observation of Spectral Modulations for X-ra
 y Point Sources. JCAP\, 07:005\, 2017. doi:10.1088/1475-7516/2017/07/005.\
 n\nhttps://indico.bitp.kiev.ua/event/18/contributions/544/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/544/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Resetting search for multiple targets
DTSTART;VALUE=DATE-TIME:20260923T140000Z
DTEND;VALUE=DATE-TIME:20260923T142000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-543@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Leonid Christophorov (Bogolyubov Institute for Theor
 etical Physics\, NAS Ukraine)\nResearch into stochastic processes with res
 etting is currently in a phase of intensive development. After the initial
  period\, when the main effects of optimizing target search in basic rando
 m walk models were identified\, researchers moved on to studying more comp
 lex problems with a focus on their practical aspects. One example is the p
 rocess of sequentially locating/destroying multiple targets by a random wa
 lker\, as a prototype of the DNA repair process.\n	\nIn this report\, we s
 how that such a process can be fully described in terms of the theory of r
 andom walks with resetting along a one-dimensional lattice with a single t
 arget that we developed earlier [1]. For the case of clusters of targets l
 ocated at lattice nodes\, exact analytical expressions for the mean times 
 Тm of the consecutive annihilation of all *m* targets\, as well as a recu
 rsive relationship\, are found. Calculations show that in certain topologi
 es of the model\, the counter-intuitive effect of accelerated annihilation
  with increasing *m*\, Т*m*  1 in both infinite and finite chains. In the
  latter\, the effect is present even in the absence of resetting. We analy
 se in detail the nature of this effect and show that it is not generated b
 y Poissonian resetting\, which rather weakens the effect\, but by the stat
 istical properties of random walks [2].\n\nThe work is performed within th
 e Project 0121U109816 of the NAS of Ukraine. Partial support from the Simo
 ns Foundation is gratefully acknowledged.\n	\n1. L.N. Christophorov. J. Ph
 ys. A: Math. Theor. 54\, 015001 (2021)\; J. Phys. A: Math. Theor. 55\, 155
 006 (2022)\; Ukr. J. Phys. 69\, 591 (2024).\n2. L.N. Christophorov. J. Phy
 s. A: Math. Theor. 59\, 015002 (2026).\n\nhttps://indico.bitp.kiev.ua/even
 t/18/contributions/543/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/543/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Non-identical particle femtoscopy as a probe of the heavy-ion coll
 ision dynamics
DTSTART;VALUE=DATE-TIME:20260923T095000Z
DTEND;VALUE=DATE-TIME:20260923T101000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-542@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Volodymyr Shapoval (Bogolyubov Institute for Theoret
 ical Physics)\nThe momentum correlations in pairs of non-identical particl
 es produced in heavy-ion collisions can be used to determine the space-tim
 e asymmetries in the radiation of the two particle species [1]. And these 
 asymmetries\, in turn\, reflect the peculiarities of the underlying collis
 ion dynamics.\n\nSince the system created in a relativistic heavy-ion coll
 ision undergoes collective expansion\, one of the explanations for the dif
 ference in average position and time of emission for different hadron spec
 ies could be the different shift by the transverse collective flow. The ot
 her possible reasons include the different particle interaction cross sect
 ions\, production via long-lived resonance decays\, re-scattering at the h
 adronic stage of the collision\, etc. [2]. However\, in the experiment one
  can hardly separate one factor from another to trace their respective rol
 es in gaining the observed result. That is why to analyze the situation in
  detail one should rather consider the simulation of the collision in real
 istic models\, where one can fully control the process.\n\nIn this work\, 
 we analyzed correlations in pion-kaon pairs based on the simulations of le
 ad-lead collisions at the Large Hadron Collider in the well-known iHKM [3]
  and LQTH [4] models. The results were compared to the experimental data f
 rom the ALICE Collaboration [2]. The analysis was carried out at different
  average pair transverse velocities. The sizes of the particle emission so
 urces and the displacements between the pion and kaon source centers were 
 determined. It was found that the crucial factor affecting the emission as
 ymmetry between pions and kaons are hadronic re-scatterings at the late ``
 afterburner'' stage of the system's evolution. The presence of a hadron ca
 scade stage simulation in the iHKM model allows it to provide a much bette
 r description of the data as compared to the LQTH model\, which lacks the 
 corresponding stage.\n\n[1] R. Lednicky\, V. L. Lyuboshits\, B. Erazmus\, 
 D. Nouais\,\nPhys. Lett. B **373**\, 30 (1996)\; A. Kisiel\, Phys. Rev. C 
 **81**\, 064906 (2010).\n[2] S. Acharya\, *et al.* (ALICE collaboration)\,
  Phys. Lett. B **813**\, 136030 (2021).\n[3] V. Yu. Naboka\, Iu. A. Karpen
 ko\, Yu. M. Sinyukov\, Phys. Rev. C **93**\, 024902 (2016).\n[4] P. Bozek 
 and I. Wyskiel-Piekarska\, Phys. Rev. C **85**\, 064915 (2012).\n\nhttps:/
 /indico.bitp.kiev.ua/event/18/contributions/542/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/542/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Equation of State of Strongly Interacting Matter from Physics-Info
 rmed Neural Networks
DTSTART;VALUE=DATE-TIME:20260923T073000Z
DTEND;VALUE=DATE-TIME:20260923T075000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-541@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Musfer Adzhymambetov (Bogolyubov Institute for Theor
 etical Physics)\nUnderstanding the properties of strongly interacting matt
 er is one of the central challenges in high-energy physics. In heavy-ion c
 ollisions\, nuclei are smashed together at relativistic speeds to recreate
  extreme conditions of temperature and density\, briefly producing a state
  of matter known as the quark-gluon plasma. This hot\, dense matter behave
 s as a nearly perfect liquid — flowing with remarkably low viscosity —
  and is best described by relativistic hydrodynamics\, whose key input is 
 the equation of state encoding the system's thermodynamic properties.\n\nT
 he underlying theory\, quantum chromodynamics\, cannot yet be solved from 
 first principles across the full phase diagram. Lattice QCD is reliable on
 ly at low baryon chemical potential\, while the hadron resonance gas model
  holds only at low particle densities. Between them lies a critical gap 
 — one that coincides precisely with the region being probed by next-gene
 ration experiments such as RHIC BES\, FAIR\, and CBM.\n\nIn this talk\, I 
 present a neural-network approach to bridging this gap. The network is tra
 ined to reproduce lattice QCD and hadron resonance gas thermodynamics in t
 heir regimes of validity\, while extrapolating into the uncharted high-bar
 yon-density region in a manner that remains thermodynamically consistent 
 — enforced through convexity-preserving architecture and derivative cons
 traints\, in the spirit of physics-informed neural networks. The result is
  a four-dimensional equation of state\, $P(T\, μ_B\, μ_Q\, μ_S)$\, span
 ning the full phase space relevant to heavy-ion collisions. I will conclud
 e by showing how this equation of state is implemented within a full relat
 ivistic hydrodynamic simulation framework.\n\nThis work was partially supp
 orted by the National Research Foundation of Ukraine (project № 2025.07/
 0050).\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/541/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/541/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Irregular conformal field theory and Painlevé equations
DTSTART;VALUE=DATE-TIME:20260924T090000Z
DTEND;VALUE=DATE-TIME:20260924T092000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-540@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Nikolai Iorgov (Bogolyubov Institute for Theoretical
  Physics)\nIn this talk\, a notion of irregular conformal blocks in two-di
 mensional conformal\nfield theory will be presented. It is expected that s
 uch irregular conformal blocks are related to the isomonodromic tau functi
 ons of Painlevé equations. I will consider\, as an example\, the Painlev
 é I equation and give details of the relation to irregular conformal fiel
 d theory.\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/540/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/540/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Generic regularity of the two-component Novikov equation
DTSTART;VALUE=DATE-TIME:20260924T114000Z
DTEND;VALUE=DATE-TIME:20260924T120000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-539@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yan Rybalko (B.Verkin Institute for Low Temperature 
 Physics and Engineering of the National Academy of Sciences of Ukraine)\nT
 his talk concerns the Cauchy problem for the following two-component Novik
 ov system:\n$\\begin{align}\n&m_t+(uvm)_x+u_xvm=0\,\n&& m=m(t\,x)\,\\\,u=u
 (t\,x)\,\\\,v=v(t\,x)\,\\\\\n&n_t+(uvn)_x+uv_xn=0\,\n&& n=n(t\,x)\,\\\\\n&
 m=u-u_{xx}\,\\\,\\\,n=v-v_{xx}\,\n&& u\,v\\in\\mathbb{R}\,\\quad\nt\,x\\in
 \\mathbb{R}\,\n\\end{align}$\n\nIt is well-known that this system admits t
 he wave-breaking phenomena: the slope of solution corresponding to the smo
 oth initial data can blow-up in finite time.\n\nThe goal is to establish t
 he generic regularity for the two-component Novikov system. More in detail
 \, we show that there exists an open dense subset of initial data\, such t
 hat the corresponding global weak solutions (which exist beyond blow-up) r
 etain certain regularity properties in the $t\,x$ plane. Applying the Bres
 san and Chen's approach [1]\, originally developed for the nonlinear varia
 tional wave equation\, we prove the following result [2].\n\n**Theorem.** 
 Consider the regular initial data $(u_0\,v_0)$ in the metric space $\\Upsi
 lon^k\\subset\\left(C^k\\right)^2\\cap\\left(H^1\\right)^2$\, $k\\geq5$\, 
 see [2] for details. Then for any $T>0$ there exists an open in $\\Upsilon
 ^k$ and dense in $\\Upsilon^{k-1}\\cap C^k_{\\mathrm{loc}}$ subset $\\math
 cal{M}_T\\subset\\Upsilon^k$\, such that for any initial data $(u_0\,v_0)\
 \in\\mathcal{M}_T$ the corresponding global weak solution $(u\,v)(t)$ sati
 sfies the following regularity properties. There exist two sets of piecewi
 se $C^{k-1}$ curves\, say $\\left\\{\\mathbf{C}_i^W\\right\\}_{i=1}^{N_1}\
 , \\left\\{\\mathbf{C}_j^Z\\right\\}_{j=1}^{N_2}\\subset[-T\,T]\\times\\ma
 thbb{R}$\, such that\n\n - both components $u$ and $v$ are $C^k$ regular a
 way from the characteristic sets $\\mathbf{C}_i^W$ and $\\mathbf{C}_j^Z$\n
  - $u$ is of class $C^1$ along each $\\mathbf{C}_j^Z$ and $v$ is of class 
 $C^1$ along each $\\mathbf{C}_i^W$.\n\n\n\n[1] A. Bressan\, G. Chen. Gener
 ic regularity of conservative solutions to a nonlinear wave equation. Ann.
  I. H. Poincaré 34 (2017) 335--354.\n[2] K.H. Karlsen\, Ya. Rybalko. Gene
 ric regularity and Lipschitz metric for a two-component Novikov system. ar
 Xiv :2512.13305v2 (2026).\n\nhttps://indico.bitp.kiev.ua/event/18/contribu
 tions/539/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/539/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Long-time asymptotic series for the Painleve II equation: Riemann-
 Hilbert approach
DTSTART;VALUE=DATE-TIME:20260924T092000Z
DTEND;VALUE=DATE-TIME:20260924T094000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-538@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yurii Zhuravlov (Bogolyubov Institute for Theoretica
 l Physics of the National Academy of Sciences of Ukraine)\nWe elaborate a 
 systematic way to obtain higher order contributions in the nonlinear steep
 est descent method for Riemann-Hilbert problem associated with homogeneous
  Painleve II equation. The problem is reformulated as a matrix factorizati
 on problem on two circles and can be solved perturbatively reducing it to 
 finite systems of algebraic linear equations. The method is applied to fin
 d explicitly long-time asymptotic behaviour for tau function of Painleve I
 I equation.\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/538/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/538/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Competing orders in rhombohedral N-layer graphene
DTSTART;VALUE=DATE-TIME:20260924T130000Z
DTEND;VALUE=DATE-TIME:20260924T132000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-534@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Sergei Sharapov (Bogolyubov Institute for Theoretica
 l Physics of the National Academy of Sciences of Ukraine)\nWe investigate 
 the emergence of correlated electron phases in rhombohedral $N$-layer grap
 hene due to two-valley Coulomb interactions within a low-energy $k \\cdot 
 p$ framework. Analytical expressions for Lindhard susceptibilities in intr
 a- and intervalley channels are derived\, and the critical temperatures fo
 r phase transitions are estimated using both the random phase approximatio
 n (RPA) and the parquet approximation (PA). Within RPA\, only Stoner and i
 ntervalley coherent (IVC) phases are supported\, while the PA reveals a ri
 cher phase structure including particle-particle (PP) channel instabilitie
 s. Magnetoelectric control of orbital magnetic order in crystalline rhombo
 hedral hexalayer graphene (R6G) is achieved without introducing a moire su
 perlattice. A hallmark of this magnetic order\, which implies time-reversa
 l symmetry breaking\, is a finite Hall conductance at zero magnetic field.
  We observe a non-volatile and hysteretic anomalous Hall effect that can b
 e electrically toggled by sweeping either the carrier density or the displ
 acement field.\nA model describing this behavior is proposed.\n\nA. Herasy
 mchuk\, S.G. Sharapov\, O.V. Yazyev\, Y. Zhumagulov\, Phys. Rev. B  113\, 
 035132 (2026)\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/534/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/534/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Resonant tunneling through one-point singular potentials
DTSTART;VALUE=DATE-TIME:20260924T110000Z
DTEND;VALUE=DATE-TIME:20260924T112000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-533@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Alexander Zolotaryuk ()\nIn one-dimensional quantum 
 mechanics\, shrinking a system to isolated points (set of Lebesgue's measu
 re zero) leads to exactly solvable models. These models are referred to as
  point (contact or zero-range) interactions (PIs). In these cases\,resolve
 nts and spectra of Schroedinger operators\, scattering coefficients  and o
 ther characteristics can analytically be computed. Currently\, because of 
 the rapid progress in fabricating nanoscale quantum devices\, of particula
 r importance is the point modeling of different structures like quantum wa
 veguides\, spectral filters\, or infinitesimally thin sheets.\n \nWe have 
 initiated a new project in the domain of PIs regarding a resonant tunnelin
 g through zero-range potentials being more singular than a traditional Dir
 ac's delta potential. A typical example is the distributional potential in
  the form of a spatial derivative of the delta function. \n\nUsing here a 
 very simple two-scale (two-parameter) regularization scheme\, we observe t
 hat different pathways $\\Delta'_{\\varepsilon}(x) \\to \\delta'(x)$ as $\
 \varepsilon \\to 0$ realize different PIs with the following three types o
 f boundary conditions on the wave function $\\psi(x)$: \ni)  $\\psi(-0) =\
 \psi(+0)=0$ (separated with  full reflection)\; \nii) $\\psi(+0)=\\theta_n
  \\psi(-0)\,~~\\psi'(+0) = \\theta_n^{-1}\\psi'(-0)$\, $\\theta_n \\in R$\
 , $n \\in Z$ (non-separated with resonant tunneling)\; \niii) $\\psi(+0)=\
 \theta_n \\psi(-0)\,~~\\psi'(+0) = \\alpha_n \\psi(-0)\n+\\theta_n^{-1}\\p
 si'(-0)\,$  $\\alpha_n \\in R $ (non-separated with resonant tunneling hav
 ing a single bound state at each $n$).\nFor each of these types\, the regi
 ons on the plane of two squeezing parameters are \nindicated explicitly.\n
 \n  Recent literature:\n\n1. A.V. Zolotaryuk and Y. Zolotaryuk\, ``Scatter
 ing data and bound states of \na squeezed double-layer structure''\,  *J. 
 Phys. A: Math. Theor.*  **54** (2021) \n035201\; [doi.org/10.1088/1751-812
 1/abd156][1]   \n2. Y. Zolotaryuk and A.V. Zolotaryuk\, ``Influence of a s
 queezed prewell \non tunneling properties and bound states in heterostruct
 ures''\,\n*Annals of Physics* **477** (2025) 169999\; [doi.org/10.1016/j.a
 op.2025.169999][2] \n3. Y. Zolotaryuk and A.V. Zolotaryuk\, ``Conditions f
 or perfect transmission of quantum particles across layered heterostructur
 es and resonance effects of an auxiliary well potential''\, *Front. Appl. 
 Math. Stat.* **11** (2015) 1636414\;\n[doi.org/10.3389/fams.2025.1636414][
 3]\n\n\n  [1]: http://doi.org/10.1088/1751-8121/abd156\n  [2]: http://doi.
 org/10.1016/j.aop.2025.169999\n  [3]: http://doi.org/10.3389/fams.2025.163
 6414\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/533/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/533/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stabilizing role of the dissipation effects in the dynamics of ele
 ctrosolitons in magnetic field
DTSTART;VALUE=DATE-TIME:20260922T093000Z
DTEND;VALUE=DATE-TIME:20260922T095000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-532@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Larissa Brizhik (Boglyubov Institute fr Theoretical 
 Physics)\nAnalytical [1] and numerical [2] study of the magnetic field imp
 act on the dynamics of electrosolitons\, i.e.\, charged Davydovs solitons\
 , in one-dimensional systems has shown that in the presence of the field s
 oliton velocity and acceleration attains oscillations with the frequency d
 etermined by the field. It has been shown that the impact of a magnetic fi
 eld within both approaches depends not only on the field strength\, but al
 so on the parameter values of the system which define such properties of p
 olarons like their energy\, amplitude\, width of localization. Because of 
 the non-zero acceleration soliton velocity gradually increases with time a
 nd at large times soliton starts to radiate linear sound and electromagnet
 ic waves due to which soliton loses its energy and becomes less stable.\n	
 Nevertheless\, in real situations there are always present dissipative eff
 ects. Molecular chains interact with the surrounding\, electron itself int
 eracts not only with the acoustical phonons\, but with other vibrational m
 odes\, etc.\, so that the energy dissipation has to be taken into account.
  It is shown that it can be done by adding an additional term into the cor
 responding equations of motion. In the continuum model soliton dynamics in
  the magnetic field is governed by the Modified Cubic Nonlinear Schoedinge
 r Equation with two extra terms determined by the presence of the magnetic
  field and energy dissipation. Both extra terms are small. The equation is
  solved using the nonlinear perturbation method. It is shown that with inc
 reasing soliton velocity due to magnetic field energy dissipation increase
 s and as a result\, soliton acceleration decreases and its dynamics is sta
 bilized. \nThe obtained results demonstrate that soliton dynamics remains 
 stable even in relatively strong magnetic fields. Therefore\, solitons can
  provide effective long-range electron transport in biological systems and
  novel low-dimensional functional materials used in modern nano- and biote
 chnologies.\n\nAcknowledgment\nThis work was done in frame of the project 
 of the National Academy of Sciences of Ukraine “Properties of low-dimens
 ional materials in the presence of external perturbations\, structural def
 ects and topological states”\, registration number 0122U000887\n\n\n\n[1
 ] L. Brizhik. Chaos\, Sol. Fractals 187 (2024) 115459 https://doi.org/10.1
 016/j.chaos.2024.115459.\n[2] L. Brizhik B.M.G. Piette\,  Chaos\, Sol. Fra
 ctals 208 (2026) 118339 https://doi.org/10.1016/j.chaos.2026.118339\n\nhtt
 ps://indico.bitp.kiev.ua/event/18/contributions/532/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/532/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Entanglement in parameterized quantum circuits and its quantificat
 ion on quantum computers
DTSTART;VALUE=DATE-TIME:20260922T122000Z
DTEND;VALUE=DATE-TIME:20260922T124000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-530@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Khrystyna Gnatenko (Ivan Franko National University 
 of Lviv)\nEntanglement in parameterized quantum circuits and its quantific
 ation on quantum computers  \n\nKh. P. Gnatenko\n\nIvan Franko National Un
 iversity of Lviv\, Professor Ivan Vakarchuk Department for Theoretical Phy
 sics\, 12 Drahomanov St.\, Lviv\, 79005\nSoftServe Inc.\, 2d Sadova St.\, 
 79021 Lviv\, Ukraine  \n\n\nWe study entanglement in multi-qubit variation
 al quantum circuits with different structures of entangling blocks. For tw
 o- and multi-qubit variational states generated by circuits with $RY$ gate
 s and entangling $CZ$ operators\, we derive analytical expressions and rec
 urrence relations for quantum correlators and the entanglement distance [1
 ]. For a closed one-dimensional chain of n qubits\, an explicit analytical
  expression for the entanglement of a qubit with the rest of the system fo
 r a two-layer variational protocol is obtained.  It is shown that the enta
 nglement of a given qubit is determined not only by its local gate paramet
 ers but also by the parameters of the gates acting on its nearest and next
 -nearest neighbors [1]. We also consider multi-qubit variational states re
 presented by vertex- and edge-weighted graphs and constructed using single
 -layer circuits with $RX$ rotations and $RZZ$  gates. For quantum graph st
 ates of arbitrary structure\, we derive the geometric measure of entanglem
 ent and quantum correlators and establish their relation to the edge- and 
 vertex-weight structure in the neighborhoods of the corresponding graph ve
 rtices [2]. We show that the entanglement of a qubit in quantum graph stat
 es is determined by the weights of the incoming and outgoing edges associa
 ted with the corresponding vertex\, as well as by its indegree and outdegr
 ee [3]. \nThe analytical results are validated using quantum computing on 
 the IBM Marrakesh and IBM Kingston quantum processors and the Qiskit AerSi
 mulator\, including noisy simulations [1-3]. The corresponding quantum cir
 cuits are implemented to investigate the dependence of the entanglement me
 asures on circuit parameters and graph structure. The results of quantum c
 omputing are in a good agreement with the analytical results..\nIt is wort
 h noting that the obtained dependencies of entanglement in variational qua
 ntum states on the parameters of variational quantum circuits and the stru
 cture of their entangling blocks are of fundamental importance. At the sam
 e time\, they are relevant to potential applications in quantum computing.
  Variational quantum states and quantum graph states underly  in a wide ra
 nge of quantum algorithms\, including quantum machine learning\, variation
 al quantum protocols\, and quantum error correction. The analytical charac
 terization of their entanglement\, together with quantum protocols for its
  quantification using quantum computing\, can therefore contribute to the 
 design and improvement of quantum algorithms and to the identification of 
 circuit architectures capable of generating and controlling a desired degr
 ee of entanglement. Also\, the obtained relations between entanglement of 
 quantum graph states and structural properties of graphs\, vertex and edge
  weights\, open up the possibility of studying them using quantum computin
 g.\n\n[1] Kh. P. Gnatenko\, A. Kaczmarek Properties of multi-qubit variati
 onal quantum states representing weighted graphs and their computing with 
 quantum programming\, \narXiv:2604.00958 (2026).\n[2] Kh. P. Gnatenko\, R.
  O. Hredil\, V. Y. Pinchuk\, M. Z. Seniak\, Y. T. Shevchuk Entanglement di
 stance of two- and multi-qubit variational states and its quantification w
 ith quantum computing\, arXiv:2605.00259  (2026).\n[3] Kh. P. Gnatenko Ent
 anglement of multi-qubit states representing directed networks and its det
 ection with quantum computing Phys. Lett. A 521\, 129815 [5 p.] (2024).\n\
 nhttps://indico.bitp.kiev.ua/event/18/contributions/530/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/530/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Criticality of structurally-disordered spin systems with weak long
 -range interactions
DTSTART;VALUE=DATE-TIME:20260922T085000Z
DTEND;VALUE=DATE-TIME:20260922T091000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-527@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Maxym Dudka (Yukhnovskii Institute of Condensed Matt
 er Physics\, National Academy of Sciences of Ukraine\, 79011 Lviv\, Ukrain
 e\;	${\\mathbb L}^4$ Collaboration \\& Doctoral College for the Statistica
 l Physics of Complex Systems\, Leipzig-Lorraine-Lviv-Coventry\, Europe\;	L
 viv Polytechnic National University 79013 Lviv\, Ukraine)\nStudies of low-
 temperature ordering in long-range interacting many-particle systems conti
 nue to attract significant interest. While such systems are common in natu
 re\, some features of their critical behavior remain unexplained. We addre
 ss the combined impact of weak structural disorder  and weak long-range in
 teractions  decaying in $d$-dimensional space as $x^{-d-\\sigma}$ with $\\
 sigma > 0$ on the critical behavior of classical  model with $n$-component
  spins.  Whithin specific regions of the parameter space $(n\, d\, \\sigma
 )$\, this model exibits a distinct disorder-induced long-range universalit
 y class. To characterize this universality class we calculate the marginal
  dimensions [1] and scaling  exponents [2\,3] governing the system's criti
 cality within the three-loop approximation of field-theoretical renormaliz
 ation group approach. Furthermore\, we present refined estimates of these 
 universal quantities by applying resummation techniques to the divergent p
 erturbation series.\n\nM.D. and D.S. acknowledge  support of the U. S. Dep
 artment of Energy (DOE)\, Office of Science\, Basic Energy Sciences\, Mate
 rials Science and Engineering Division\, under Award No. DE–SC0013599\n\
 n[1] D. Shapoval\, M. Dudka\, Yu. Holovatch\, *Low Temp. Phys.* $\\textbf{
 48}$ (2022) 1049.\n[2]  M. Dudka\, D. Shapoval\, Yu. Holovatch\, *Journal 
 of Physical Studies* $\\textbf{28}$ (2024) 2601.\n[3] D. Shapoval\, M. Dud
 ka\, *Condens. Matter Phys.* $\\textbf{28}$ (2025) 43503.\n\nhttps://indic
 o.bitp.kiev.ua/event/18/contributions/527/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/527/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quasi-Linkage Equilibrium in spatially separated populations and i
 n diploid genetics
DTSTART;VALUE=DATE-TIME:20260922T082000Z
DTEND;VALUE=DATE-TIME:20260922T085000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-525@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Erik Aurell (Department of Computational Science and
  Technology\, KTH-Royal Institute of Technology\, AlbaNova University Cent
 er)\nQuasi-Linkage Equilibrium (QLE) is a theory developed by Kimura (1965
 ) and Neher & Shraiman (2009:2011) to explain the emergency of distributio
 ns of genotypes in a population akin to the canonical ensemble in statisti
 cal physics\, referred to as a QLE state. Recombination (exchange of genet
 ic material between individuals) acts analogously to molecular collisions 
 in kinetic gas theory\, and leads\, if strong enough\, to relaxation to an
  equilibrium-like state\, for a review\, see [1].\n\nGeographic isolation 
 is important in evolution\, it is a driving force behind speciation. I wil
 l discuss how recombination interacts with migration between spatially iso
 lated sub-populations\, and if the QLE state can coexist with migration. I
  will also consider the setting where different sub-populations live in di
 fferent environments with different fitness landscapes\, and if one can in
 fer those landscapes from the population structures if individuals can mov
 e between the populations [2]. I will also discuss the conceptual issue if
  the assumption of haploid genomes usually made in the literature is only 
 a simplification or if the evolution of diploid populations is qualitative
 ly different and can lead to other phases than QLE.\n\n[1] "Statistical ge
 netics in and out of quasi-linkage equilibrium"\, V Dichio\, HL Zeng\, E A
 urell\, Reports on Progress in Physics 86 (5)\, 052601 (2023)\n[2]  "Fitne
 ss Inference in Presence of Migrations between Coupled Evolving Population
 s"\, YH Huang\, B Dumont\, HL Zeng\, J Barton\, E Aurell (2026)\, arXiv pr
 eprint arXiv:2605.22665\n\nhttps://indico.bitp.kiev.ua/event/18/contributi
 ons/525/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/525/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Magnons as uncharged carriers for quantum communication between na
 nomagnets
DTSTART;VALUE=DATE-TIME:20260923T142000Z
DTEND;VALUE=DATE-TIME:20260923T144000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-524@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Serhii Tunyk (Bogolyubov Institute for Theoretical P
 hysics\, National Academy of Sciences of Ukraine)\nRecent experimental stu
 dies have shown that magnonics—an independent branch of spintronics—ca
 n realize its potential in nanotechnology applications involving magnetoph
 otonics\, thermal nanoconversion\, magnonic capacitors\, magnonic transist
 ors\, and other fields. Magnons are very good candidates for use in quantu
 m communication. This is because the transport of magnons as uncharged qua
 siparticles can occur without the generation of Joule heat\, and\, just as
  with charged carriers\, this transport can be controlled using magnetic a
 nd electric fields. We propose a physical mechanism whereby a localized sp
 in excitation (Kittel magnon) generated in one microwave cavity can be res
 onantly transferred to another cavity via a ferromagnetic chain connecting
  the nanomagnets embedded in the cavities. It is shown that long-range mag
 non transfer can be achieved via coherent one-step tunneling of magnons be
 tween nanomagnets. Our theoretical study is based on a model in which\, fo
 r fixed nanomagnet spin values\, the states are determined by macrospin pr
 ojections\, and the ferromagnetic chain acts as a mediating scattering cen
 ter. The coupling between spin excitations in the "nanomagnet A - ferromag
 netic chain - nanomagnet B" hybrid structure (AFB structure) is mediated b
 y the Heisenberg exchange interaction between the spins of adjacent parama
 gnetic units of the structure. Based on this model\, analytical formulas w
 ere derived that made it possible to understand the physics of controlling
  magnon flow using magnetic fields\; these fields tune the Kittel magnon f
 requency to the frequencies of delocalized magnons in the AFB structure. T
 he main results of the study include the following. Analytical expressions
  for the magnon transport rate and magnon flow are obtained and key parame
 ters controlling off-resonant and resonant magnon tunneling regimes are in
 dicated. Physical conditions are determined under which peak values of the
  rate characterizing the process of resonant transmission of the Kittel ma
 gnon arise both at a fixed tunneling energy with an arbitrary number of un
 its in the ferromagnetic chain or at a fixed number of chain units with a 
 changing tunneling energy. A mechanism of coherent transfer is proposed\, 
 based on the premise that the spin states of a bridge\, containing magneti
 cally ordered paramagnetic units\, play a virtual role. This facilitates a
  specific quantum exchange of magnons both within the bridge and between i
 ts terminal units and the adjacent nanomagnets. As a result\, a long-range
  superexchange coupling arises between magnetostatic spin excitations\, wh
 ich ensures a tunnel regime of magnon transport between nanomagnets. It wa
 s also shown that due to the strong photon-magnon coupling in the microwav
 e  cavity\, at a certain magnetic field\, the tunneling flow of magnons ca
 n reach an additional peak value\, which reflects the process of resonant 
 photon-to-magnon conversion [1]. The obtained results indicate the potenti
 al for using magnons for quantum communication in hybrid structures where 
 the transduction of one type of quasiparticle into another (in our case\, 
 photons and magnons) is possible.\n\nThis work is partialy supported by th
 e project of the Ministry of Education and Science of Ukraine «Developmen
 t of theoretical and computational methods for the study of micro- and mac
 rosystems in quantum technology”\n\n[1] E. G. Petrov\, S. M. Tunyk\, V.V
 . Gorbach\, Phys. Rev. Appl.\, 25\, 024072 (2026).\n\nhttps://indico.bitp.
 kiev.ua/event/18/contributions/524/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/524/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Particle multiplicity fluctuations of quantum origin and   high-mu
 ltiplicity pp collision events
DTSTART;VALUE=DATE-TIME:20260923T075000Z
DTEND;VALUE=DATE-TIME:20260923T081000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-523@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Sergiy Akkelin (Bogolyubov Institute for Theoretical
  Physics of the National Academy of Sciences of Ukraine)\nThe multiplicity
  dependence of the two-particle Bose-Einstein momentum correlation radii i
 n pp collisions at the LHC has been measured at a fixed energy of collisio
 ns. One notable feature of these measurements is that the effective system
 ’s volume\, when extracted from the correlation radius parameters\, appe
 ars to scale nearly linearly with charged-particle multiplicity [1-3]\, ex
 cept for low multiplicities where initial state effects dominate and\, qui
 te unexpectedly\, except for very high multiplicities where\, at variance 
 with the expected behavior for emission from hydrodynamically expanding sy
 stems\, one sees systematic deviations from such a scaling behavior. That 
 is\, the striking feature of the data is that the correlation radius param
 eters become approximately independent of the particle multiplicity in the
  limit of very high multiplicities [1\,2]. The question naturally arises: 
 How can this controversy with hydrodynamics be resolved?\nIn Ref. [4]\, we
  argue that quantum-origin multiplicity fluctuations dominate the fluctuat
 ions in particle multiplicity in high-multiplicity pp collision events at 
 a fixed LHC energy. The quantum-to-classical transition of multiplicity fl
 uctuations happens when the interference term between the corresponding st
 ates becomes negligible. Until this happens\, superposition cannot be inte
 rpreted as a classical ensemble of its component states. To connect quantu
 m fluctuations of particle multiplicity to event-by-event multiplicity flu
 ctuations\, we introduce the statistical ensemble of the multiplicity fluc
 tuations of particles after the system’s freeze-out. We utilize the maxi
 mum entropy prescription to determine a quantum state at kinetic freeze-ou
 t and derive expressions for multiplicity-selected particle momentum spect
 ra and correlation functions by applying a fixed particle-number constrain
 t to this state. Then\, we study how multiplicity fluctuations at high mul
 tiplicities impact the multiplicity-selected particle momentum spectra and
  correlation functions. In particular\, we find that the effective system
 ’s volume should become approximately independent of the particle multip
 licity in the limit of very high multiplicities in multiplicity-selected c
 ollision events.\n\n\nReferences\n\n[1] ATLAS Collaboration\, Eur. Phys. J
 . C 75\, 466 (2015)\, https://doi.org/10.1140/epjc/s10052-015-3644-x\; 82\
 , 608 (2022)\,  https://doi.org/10.1140/epjc/s10052-022-10472-0 .\n[2] A. 
 M. Sirunyan et al. (CMS Collaboration)\, Phys. Rev. C 97\, 064912 (2018)\,
  https://doi.org/10.1103/PhysRevC.97.064912 \;  J. High Energy Phys. 03 (2
 020) 014\, https://doi.org/10.1007/JHEP03(2020)014 .\n[3] S. Acharya et al
 . (ALICE Collaboration)\, Phys. Rev. C 109\, 024915 (2024)\, https://doi.o
 rg/10.1103/PhysRevC.109.024915 .\n[4] S.V. Akkelin\, Phys. Rev. D 112\, 11
 6007 (2025)\,  https://doi.org/10.1103/k7mv-57bt .\n\nhttps://indico.bitp.
 kiev.ua/event/18/contributions/523/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/523/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Spectrum of electron states in a charged atomic chain within the D
 irac description
DTSTART;VALUE=DATE-TIME:20260924T132000Z
DTEND;VALUE=DATE-TIME:20260924T134000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-520@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Alexander Eremko (Bogolyubov Institute for Theoretic
 al Physics of the National Academy of Sciences of Ukraine)\nIt is demonstr
 ated that the description of electron states in a one-dimensional crystal 
 with account of electron spin should be based on the Dirac theory. Electro
 n spin states are determined by the eigen states of the spinor invariants 
 with their free parameters. \n\nIt is shown that in the case of atomic cha
 in with the cylindric symmetry integrals of motion include a set of spinor
  operators corresponding to different spin states. Electrons bound by a ch
 arged atomic chain\, are shown to attain one-dimensional character of moti
 on and can have arbitrary spin orientation corresponding to the particular
  chosen spinor invariant. The general solution of the Dirac equation for a
  one-dimensional crystal is obtained analytically and is shown to be indep
 endent of the choice of the spinor invariant(s). It includes free paramete
 rs which have the meaning of spin variables and can be fixed corresponding
  to the concrete spinor invariants determined by the symmetry of the syste
 m and experiment conditions.\n\nThe spectrum of bound electrons in atomic 
 chain is calculated. The electron band structure is shown to be characteri
 zed by the principal quantum number *n* so that the corresponding energy b
 ands are split into *n* subbands describing their fine structure.\n\nhttps
 ://indico.bitp.kiev.ua/event/18/contributions/520/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/520/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The exact expression for increasing selectivity through statistica
 l fluctuations in a system with a threshold
DTSTART;VALUE=DATE-TIME:20260924T081000Z
DTEND;VALUE=DATE-TIME:20260924T083000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-518@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksandr Vidybida (Bogolyubov Institute for Theoret
 ical Physics)\nIn various statistically defined situations\, like referend
 um\, epidemic threshold\, mass service process or a chemical sensor the pr
 obability of overall output coincides with the probability that a threshol
 d $N_0$ number of elementary events has been achieved. The latter depends 
 on the probability $p$ that a single elementary event happens. Elementary 
 event for a referendum case is the positive vote of a single voter\; for a
  chemical sensor $-$ is the ligand binding by a single receptor in the sen
 sor. The probability $p$ of elementary event may depend on some external f
 actor $-$ campaigning type L for the referendum case\, or the ligand type 
 L applied in the case of chemical sensor. This constitutes the selectivity
  of elementary event. Naturally\, the probability that the threshold $N_0$
  is achieved depends on L as well. This constitutes the selectivity of ess
 ential event. Any of the two selectivities can be expressed by means of a 
 dimensionless non-negative number. We derive a concise mathematical expres
 sion\, for comparing the two selectivities\, based on the incomplete beta-
 function\, or on a continued fraction. Possible application in a chemical 
 sensor is discussed.\n\nhttps://indico.bitp.kiev.ua/event/18/contributions
 /518/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/518/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nuclear deflagration phenomenon and prospective concept of safe fa
 st breeder reactor
DTSTART;VALUE=DATE-TIME:20260922T074000Z
DTEND;VALUE=DATE-TIME:20260922T082000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-517@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Sergii Fomin (AITP NSC KIPT)\nThis review discusses 
 the physical nature and conditions governing the phenomenon of slow nuclea
 r burning in a breeding medium - “nuclear deflagration”- specifically 
 in the breeding zone of a fast breeder reactor. A brief overview is provid
 ed of various theoretical approaches to describing this phenomenon and the
  results obtained based on them [1–4]. The results of our study of the n
 uclear deflagration in the form of nuclear burning wave are presented. Thi
 s study is based on an original deterministic approach that relies on the 
 numerical solution of a non-stationary\, nonlinear\, multi-group neutron d
 iffusion equation in conjunction with a system of fuel nuclide burnup equa
 tions and equations of nuclear kinetics of precursors of delayed neutrons 
 [5–7]. The unique “intrinsic safety” properties and other advantages
  of a promising fast breeder reactor operating in a nuclear burning wave m
 ode are discussed\; the main parameters of such a reactor are presented\; 
 and problematic issues and possible solutions are addressed.\nThe research
  is part of the TREASURE coordinated research project under the EURATOM pr
 ogram (Project No. 101164616)\, which is being carried out from 2024 to 20
 28.\n\n1. L.P. Feoktistov. Preprint IAE-4605-4\, 1988\; Sov. Phys. Doklady
 \, 34 (1989) 1071.\n2. V.Ya. Gol’din and D.Y. Anistratov. Sov. Journ. Ma
 thematical Modeling\, 7:10 (1995) 12.\n3. E. Teller. Nuclear Energy for th
 e Third Millennium. Preprint UCRL-JC-129547\, LLNL\, 1997.\n4. H. Sekimoto
 \, K. Ryu\, Y. Yoshimura. Nuclear Science and Engineering\, 139 (2001) 306
 .\n5. S.P. Fomin et al. Annals of Nuclear Energy\, 32 (2005) 1435\; 148 (2
 020) 107699. \n6. S.P. Fomin et al. Progress in Nuclear Energy\, 50 (2008)
  163\; 53 (2011) 800.\n7. S.P. Fomin et al. Proc. Intern. Conf. on Fast Re
 actors & Related Fuel Cycle\, Paris\, France\, 2013\, paper CN-199-457\; V
 ienna\, Austria\, 2022\, paper CN-291-365.\n\nhttps://indico.bitp.kiev.ua/
 event/18/contributions/517/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/517/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Manifestation of bilinear flexo-antiferrodistortive coupling at tw
 ins and antiphase boundaries in ferroelastics
DTSTART;VALUE=DATE-TIME:20260924T123000Z
DTEND;VALUE=DATE-TIME:20260924T130000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-512@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Anna Morozovska (Інститут фізики НА
 Н України)\nThe flexoelectric-type coupling between the gradients 
 of electric polarization\, described by a true polar vector $\\vec{P}$\, a
 nd the antiphase rotation of structural groups\, described by an axial pse
 udovector $\\vec{\\Phi }$\, can lead to the appearance of interfacial pola
 rization at the twin walls\, antiphase boundaries and surfaces of antiferr
 odistortive (AFD) ferroelastics [1]. The linear-quadratic flexo-AFD coupli
 ng may contribute significantly to observable interfacial polarization ind
 uced by oxygen octahedral rotations at the antiphase boundaries and/or twi
 n walls in YMnO3\, Ca3Mn2O7\, CaTiO3 and SrTiO3\, as well as lead to the a
 ppearance of versatile spatially modulated structures in multiferroics [1]
 .\nThe quadratic dependence of the linear-quadratic flexo-AFD coupling ene
 rgy on $\\vec{\\Phi}$ appeared principally important for the emergence of 
 interfacial polarization\, because the odd powers of anti-phase (i.e.\, si
 gn-alternating in neighboring sublattices) pseudovector $\\vec{\\Phi }$ ca
 nnot induce the continuous polarization of structural domain walls\, surfa
 ces or interfaces in AFD ferroelastics. Therefore\, it seemed that it made
  little sense to consider odd powers of $\\vec{\\Phi }$ when constructing 
 the sublattice-insensitive flexo-AFD coupling energy. However\, recently V
 isser et al. [2] and Fang et al. [3] proposed the concept of alterelectric
 ity\, an electrical analogue of altermagnetism\, in which two switchable s
 tates possess alternating band structures. \nUsing the Landau-Ginsburg-Dev
 onshire approach we show that the linear gradient-type coupling between th
 e electric polarization vector $\\vec{P}$ and antiferrodistortive long-ran
 ge order parameter pseudovector $\\vec{\\Phi }$\, that has the form of Lif
 shitz invariant $\\left(\\vec{P}\\bullet \\mathrm{\\nabla }\\times \\vec{\
 \Phi }\\\; -\\vec{\\Phi }\\bullet \\mathrm{\\nabla }\\times \\vec{P}\\righ
 t)/2$ and named “bilinear flexo-antiferrodistortive coupling”\, can em
 erge in all antiferrodistortive ferroelastics\, since it is symmetry-allow
 ed [4]. Using the four sublattices model we reveal that the bilinear flexo
 -antiferrodistortive coupling can induce the sublattice-sensitive polariza
 tion at the twin walls and antiphase boundaries in antiferrodistortive fer
 roelastics without any ferroelectric or antiferroelectric ordering. Since 
 the induced polarization $\\vec{\\delta P}$ is perpendicular to $\\vec{\\P
 hi}$ and counter-directed in neighboring sublattices with checkerboard-typ
 e direction of $\\vec{\\Phi}$\, such structure of $\\vec{\\delta P}$ may c
 orrespond to the alterelectric-type quadrupolar electric order. However\, 
 physical manifestations of the bilinear flexo-antiferrodistortive coupling
  are invisible in most nanostructured antiferrodistortive ferroelectrics a
 nd antiferroelectrics due to the domination of piezoelectric and/or omnipr
 esent linear flexoelectric couplings. We have shown that the bilinear flex
 o-antiferrodistortive coupling can induce alterelectric-type polarization 
 near antiferrodistortive domain boundaries in ferroelastics without any fe
 rroelectric or antiferroelectric long-range ordering [1].\nAcknowledgement
 s. The work is primary supported as part of the Computational Materials Sc
 iences Program funded by the US Department of Energy\, Office of Science\,
  Basic Energy Sciences\, under Award Number DE-SC0020145. The part of A.N.
 M. and E.A.E. efforts is also supported by National Academy of Sciences of
  Ukraine (grants No. 5.8/26-П\, 1.4.B/222\, III-6-26). \n[1]. A.N. Morozo
 vska\, E.A. Eliseev\, M.D. Glinchuk\, L.-Q. Chen\, V. Gopalan. Interfacial
  Polarization and Pyroelectricity in Antiferrodistortive Structures Induce
 d by a Flexoelectric Effect and Rotostriction. Phys.Rev. B. 85\, 094107 (2
 012)\; https://doi.org/10.1103/PhysRevB.85.094107\n[2]. A. Visser\, V. Kö
 nye\, O. Janson\, J. van den Brink\, C. Coulais\, and J. van Wezel. "Multi
 polar Piezoelectricity and Anisotropic Surface Transport in Alterelectrics
 ." arXiv preprint arXiv:2604.18324 (2026)\; https://doi.org/10.48550/arXiv
 .2604.18324\n[3]. S. Fang\, J. Wang\, Z. Guo\, J. Gong\, H. Meng\, W. Wang
 \, Z. Cheng\, X. Wang\, and Y. S. Ang. "Alterelectricity: Electrical Analo
 gue of Altermagnetism." arXiv preprint arXiv:2604.07112 (2026)\; https://d
 oi.org/10.48550/arXiv.2604.07112\n[4]. E. A. Eliseev\, A. N. Morozovska\, 
 A. Saha and V. Gopalan. Bilinear Flexo-Antiferrodistortive Coupling in Fer
 roelastics: Polar Twins\, Antiphase Boundaries and Fingerprints of Alterel
 ectricity. ArXiv Preprint (2026)\; https://doi.org/10.48550/arXiv.2606.294
 56\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/512/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/512/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Strong interactions from scattering to matter: $^4$He atoms and nu
 cleons
DTSTART;VALUE=DATE-TIME:20260923T090000Z
DTEND;VALUE=DATE-TIME:20260923T093000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-511@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Ubirajara van Kolck (European Center for Theoretical
  Studies in Nuclear Physics and Related Areas)\nEffective field theories (
 EFTs) allow for a systematic description of processes at a particular ener
 gy scale\, even for strongly interacting systems where no small coupling c
 onstants exist. EFTs link scattering and matter\, topics of a great tradit
 ion of research at BITP. I will discuss two contemporary systems where str
 ucture emerges from essentially one parameter: $^4$He atoms and nucleons.\
 n\nhttps://indico.bitp.kiev.ua/event/18/contributions/511/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/511/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Staggering domino-like blast front motion in a one-dimensional col
 d gas
DTSTART;VALUE=DATE-TIME:20260922T120000Z
DTEND;VALUE=DATE-TIME:20260922T122000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-510@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yurij Holovatch (Yukhnovskii ICMP\,  NAS of Ukraine\
 , Lviv)\nThe relationship between the macroscopic dynamics of matter\, vie
 wed as a continuous medium\, and that of its microscopic corpuscular const
 ituents is a paramount challenge in physics. Its prominent 20th-century fo
 rmulation is Hilbert’s sixth problem\, which specifically calls for 'dev
 eloping mathematically the limiting processes... which lead from the atomi
 stic view to the laws of motion of continua' [1].  This applies to the tra
 nsport of energy in a cold gas following an explosion – an instant injec
 tion of energy at a certain point. In this talk\, we show that a typical a
 nd relatively simple model of this phenomenon may exhibit surprisingly cou
 nterintuitive behavior.\n\nWe study the model in which point particles wit
 h masses $m\,\\mu\, m\, \\mu\, \\dots$\,  $(m \\geq \\mu)$ are distributed
  on the positive half-line $\\mathbb{R}_{+}$. Their dynamics are initiated
  by giving a positive velocity to the leftmost particle\; in its course\, 
 the particles undergo elastic collisions. For this model with $m/\\mu=2$\,
  it has previously been established that the dynamics that start from rand
 om initial positions are consistent with predictions based on Euler's hydr
 odynamic equation [2]. In particular\, they have the following properties:
  (i) the position of the rightmost particle (shock front) evolves as $t^\\
 delta$ with $\\delta \n\nhttps://indico.bitp.kiev.ua/event/18/contribution
 s/510/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/510/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Physical modeling of macroscopic properties of the complex many-pa
 rticle\, poly-dispersive micromechanical (granular) systems
DTSTART;VALUE=DATE-TIME:20260923T144000Z
DTEND;VALUE=DATE-TIME:20260923T150000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-508@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleg Gerasymov (Odesa National  University)\nPhysica
 l modeling of macroscopic properties of the complex many-particle\, poly-d
 ispersive micromechanical (granular) systems\nO.I. Gerasymov*\, A.Ya. Spiv
 ak#\n*State University of Intelligent Technology and Telecommunications\, 
 Odesa\n*National Technical University of Ukraine "Igor Sikorsky Kyiv Polyt
 echnic Institute\, Kyiv\nOdesa National Mechnikov’s University\nThe stud
 y of the influence on the formation of macroscopic properties of multi-com
 ponent mixtures is a complex and continuing to be an urgent task of fundam
 ental physics and its numerous applications [1]. The traditional difficult
 ies in determining reference states are supplemented by the difficulties o
 f taking into account the effect of compaction in multicomponent mixtures.
  The task of describing the relationships between the micro- and macro-par
 ameters of such systems is further complicated by the fact that multi-comp
 onent mixtures (even if they are granular) can be in various states of agg
 regation from gaseous and liquid to crystalline. \nPresented paper develop
 s theoretical approaches to the description of macroscopic (compressibilit
 y) and structural (compaction) characteristics of complex many-particle\, 
 poly-dispersive multi-component mixtures\, using Kirkwood-Buff's semi-phen
 omenological algorithm [2]\, molecular models like Carnahan-Starling-Manso
 ori [3]. Based on a comparative analysis would be build a prognostic base 
 for the practical application of the results obtained in order to optimize
  (achieve the required values) of control parameters in liquid\, granular 
 mixtures by manipulation of their composition and/or compaction. Along thi
 s line\, using the Carnahan–Starling–Mansoori hard-sphere conglomerati
 on models and the Kirkwood–Buff statistical theory\, the effect of compa
 ction (packing) on the compressibility of a binary granular mixture has be
 en analyzed [4]. The theoretical results are compared with the experimenta
 l ones obtained in alternative studies of the systems whose internal struc
 ture corresponds to the construction characteristics of the model [5]. The
  possibility of the maximum packing effect at special dispersion and mole 
 fraction values of the components has been shown. The existence of the lim
 it and intermediate states of the mixture with a predominant concentration
  of one of the components and the possibility of the most adequate descrip
 tion of the system properties in such states using one of the above-mentio
 ned approaches have been demonstrated. The interval of values for the comp
 onent volume fractions has been determined\, where both approaches well de
 scribe the data of corresponding experiments.\nReferences\n[1] O.I. Gerasy
 mov. Physics of granular materials. Odesa\, TES\, 2015. 264p.\n[2] J.G. Ki
 rkwood\, F.P. Buff. The statistical mechanical theory of solutions. I. J. 
 Chem. Phys. 19\, 774. \n[3] G.A. Mansoori\, N.F. Carnahan\, K.E. Starling\
 , T.W. Leland\, Jr. Equilibrium thermodynamic properties of the mixture of
  hard spheres. J. Chem. Phys. 54\, 1523 (1971). \n[4] O.I. Gerasymov\, A.Y
 a. Spivak. Packing and compressibility of binary micromechanical (granular
 ) systems. Ukr. J. Phys. 70\, No. 8\, 543 (2025). \n[5] S. Pillitteri\, G.
  Lumay\, E. Opsomer\, N. Vandewalle. How size ratio and segregation affect
  the packing of binary granular mixtures. Soft Matt. 16\, 9094 (2020).\n\n
 https://indico.bitp.kiev.ua/event/18/contributions/508/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/508/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The quest for the Hoyle-analog states in light hypernuclei
DTSTART;VALUE=DATE-TIME:20260923T093000Z
DTEND;VALUE=DATE-TIME:20260923T095000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-507@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Victor Vasilevsky (Bogolyubov Institute for Theoreti
 cal Physics)\nTo resolve a long-standing problem of nuclear astrophysics r
 egarding of synthesis of $^{12}$C and heavier nuclei\, in 1953\, F. Hoyle 
 suggested that the nuclei $^{12}$C were created in a collision of three al
 pha particles. This collision leads to the creation of a very narrow (long
 -lived) 0$^{+}$ resonance state\, which emits a photon and then transforms
  into a bound state of $^{12}$C. Moreover\, F. Hoyle predicted the energy 
 and width of the 0$^{+}$ resonance state with high precision. Later\, this
  assumption was experimentally confirmed and now this resonance state is c
 alled the Hoyle state. Many theoretical models have been used to describe 
 such an exotic state and to reveal its nature. A microscopic three-cluster
  method\, proposed in [1]\, has been successfully applied in [2] to study 
 the peculiarities of the Hoyle state and find the Hoyle-analog states [3] 
 in a set of light nuclei.\n\nIn the present work\, we study the resonance 
 structure of light hypernuclei $_{\\Lambda}^{6}$H\, $_{\\Lambda}^{6}$He\, 
 $_{\\Lambda}^{6}$Li\, $_{\\Lambda}^{7}$He\, $_{\\Lambda}^{7}$Li\, $_{\\Lam
 bda}^{7}$Be\, and try to find the Hoyle-analog states\, i.e.\, the long-li
 ved resonance states which can be formed in a three-cluster collision. The
  quest is performed with a three-cluster microscopic model\, which was sug
 gested in Ref. [1] and modified to study hypernuclei. The selected hypernu
 clei are considered as three-cluster systems\, where one cluster is the la
 mbda hyperon. For each hypernuclei we selected a three-cluster configurati
 on\, which has the minimal threshold energy among other three-cluster conf
 igurations. This dominant three-cluster configuration allows us to study b
 ound states of a compound hypernuclear system and its resonance states in 
 two- and three-cluster continua.\n\nIn hypernuclei $\\ _{\\Lambda}^{6}$H\,
  $_{\\Lambda}^{6}$He\, $_{\\Lambda}^{6}$Li\, $_{\\Lambda}^{7}$He\, $_{\\La
 mbda}^{7}$Li\, we found several very narrow resonance states\, their total
  width is very small\, less than 10 keV\, and they lie close to the corres
 ponding three-cluster threshold. The narrowest resonance states have wave-
 function structures typical of those of the Hoyle-analog states in ordinar
 y nuclei [3]. Thus\, the Hoyle analog states can be excited in hypernuclei
  $_{\\Lambda}^{6}$H\, $_{\\Lambda}^{6}$He\, $_{\\Lambda}^{6}$Li\, $_{\\Lam
 bda}^{7}$He\, $_{\\Lambda}^{7}$Li in triple collisions of three clusters\,
  one of which is the lambda hyperon. \nWe assume that the narrowest resona
 nce states revealed by our model can be experimentally detected.\n\n[1]. V
 . S. Vasilevsky\, A. V. Nesterov\, F.  Arickx\, J.  Broeckhove\, “Algebr
 aic model for scattering in three-s-cluster systems. I. Theoretical backgr
 ound”\, Phys. Rev. C\, vol. 63\, 034606\, 2001.\n[2]. V. S. Vasilevsky\,
  F.  Arickx\, W. Vanroose\, J.  Broeckhove\, “Microscopic cluster descri
 ption of $^{12}$C”\, Phys. Rev. C\, vol. 85\, 034318\, 2012.\n[3]. V. S.
  Vasilevsky\, K. Katō\, N.  Takibayev\, “Systematic investigation of th
 e Hoyle -analog states in light nuclei “\, Phys. Rev. C\, vol. 98\, 0243
 25\, 2018.\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/507/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/507/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Baryon fluctuation signatures of the onset of  deconfinement
DTSTART;VALUE=DATE-TIME:20260923T070000Z
DTEND;VALUE=DATE-TIME:20260923T073000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-506@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Mark Gorenstein (Bogolyubov Institute for Theoretica
 l Physics\, National Academy of Sciences of Ukraine)\nWe predict an anomal
 ous collision-energy dependence of proton-number\nfluctuations as a conseq
 uence of the onset of deconfinement in heavy-ion collisions at the nucleon
 -pair centre-of-mass energy (8 − 12) GeV. The effect arises from the cha
 nge of properties of the effective degrees of freedom during the transitio
 n from confined and deconfined matter. The proposed interpretation provide
 s a unified explanation of the collision-energy dependence of proton fluct
 uations together with the previously observed anomalies in hadron producti
 on\, and yields semi-quantitative predictions without introducing paramete
 rs adjusted to the fluctuation data.\n\nhttps://indico.bitp.kiev.ua/event/
 18/contributions/506/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/506/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Canonization-based symmetry breaking in an integrable four-compone
 nt nonlinear dynamical system on a quasi-one-dimensional lattice with back
 ground-controlled intersite coupling
DTSTART;VALUE=DATE-TIME:20260924T094000Z
DTEND;VALUE=DATE-TIME:20260924T100000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-504@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Vakhnenko Oleksiy O. (Bogolyubov Institute for Theor
 etical Physics)\nEleven years ago we developed the four-component nonlinea
 r integrable dynamical system on a ribbon of two-leg triangular lattice wi
 th the common coherent and uncommon background-controlled intersite coupli
 ngs [1\, 2]. The system can be classified as a sort of semi-discrete nonli
 near Schrödinger system. It characterized by four basic (independent) fie
 lds on zero background and two concomitant (dependent) fields on nonzero b
 ackground. Due to nonzero background values of concomitant fields the enti
 re Poisson structure of semi-discrete nonlinear system acquires essentiall
 y nonstandard form veiling the true physical interpretation of basic field
 s. Looking for a prospective physical applications of suggested semi-discr
 ete nonlinear integrable system to the modeling of transport phenomena in 
 long macromolecules or other quasi-one-dimensional physical objects\, we s
 uggested rather sophisticated multistage transformation to the semi-discre
 te nonlinear integrable system\, characterized by the canonical Poisson st
 ructure and physically motivated field functions as well as by the standar
 d canonical Hamiltonian formulation [3\, 4\, 5\, 6]. As a result\, we obta
 ined two distinct but physically equivalent realizations of canonized semi
 -discrete four-component nonlinear integrable system\, each one being mani
 fested by a pronounced symmetry breaking between the so-called strong two-
 component and weak two-component subsystems. The rate of symmetry breaking
  is governed by the nonnegatively defined background parameter µν\, so t
 hat for µν = 0 the symmetry between subsystems becomes totally restored.
  We believe\, the value of background parameter µν could be regulated by
  external conditions imposed on a lattice. For undercritical values µν  
 1 of background parameter µν each particular canonized system demonstrat
 es bright excitation regime in strong subsystem and dark excitation regime
  in weak subsystem. The crossover between the bright–bright and bright
 –dark regimes of excitation dynamics established for the case of attract
 ive nonlinearity occurs in the very critical point µν = 1.\n\nReferences
 \n[1] O.O. Vakhnenko. Integrable nonlinear Schr¨odinger system on a trian
 gular-lattice ribbon\, J. Phys. Soc. Japan 84(1)\, 014003 (12 pages) (2015
 ).\n[2] O.O. Vakhnenko. Nonlinear integrable model of Frenkel-like excitat
 ions on a ribbon of triangular lattice\, J. Math. Phys. 56(3)\, 033505 (21
  pages) (2015).\n[3] O.O. Vakhnenko. Symmetry-broken canonizations of the 
 semi-discrete integrable nonlinear Schr¨odinger system with background-co
 ntrolled intersite coupling\, J. Math. Phys. 57(11)\, 113504 (16 pages) (2
 016).\n[4] O.O. Vakhnenko. Semi-discrete integrable nonlinear Schr¨odinge
 r system with background-controlled inter-site resonant coupling\, J. Nonl
 in. Math. Phys. 24(2)\, 250–302 (2017).\n[5] O.O. Vakhnenko. Distinctive
  features of the integrable nonlinear Schr¨odinger system on a ribbon of 
 triangular lattice\, Ukr. J. Phys. 62(3)\, 271–282 (2017).\n[6] O.O. Vak
 hnenko\, V.O. Vakhnenko\, and A.P. Verchenko. Physical insight into the se
 mi-discrete nonlinear integrable systems with the true and false multicomp
 onentness\, Chaos Solitons Fractals 200(2)\, 117043 (24 pages) (2025).\n\n
 https://indico.bitp.kiev.ua/event/18/contributions/504/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/504/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Is the superfluidity of a Bose gas related to the spontaneous brea
 king of $U(1)$ symmetry?
DTSTART;VALUE=DATE-TIME:20260924T134000Z
DTEND;VALUE=DATE-TIME:20260924T140000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-503@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Maksim Tomchenko (Bogolyubov Institute for Theoretic
 al Physics)\nIt is widely accepted that phonons in a superfluid Bose gas a
 re Goldstone bosons\, and that the spontaneous breaking of $U(1)$ symmetry
  is the primary cause of superfluidity. The first statement is justified b
 y spontaneous symmetry breaking (SSB)\, which is usually defined as follow
 s: the Hamiltonian of the system is invariant under the $U(1)$ transformat
 ion $\\hat{\\Psi}(\\mathbf{r}\,t)\\rightarrow e^{i\\alpha}% \\hat{\\Psi}(\
 \mathbf{r}\,t)$\, but the order parameter $\\Psi(\\mathbf{r}\,t)$ is not. 
 However\, the strict definition of SSB is different: the Hamiltonian and t
 he boundary conditions are invariant under a symmetry transformation\, whi
 le the $\\it{ground~ state}$ is not. Based on the latter criterion\, we st
 udy a finite system of spinless\, weakly interacting bosons using three ap
 proaches: the standard Bogoliubov method\, the particle-number-conserving 
 Bogoliubov method\, and the approach based on the exact ground-state wave 
 function. Our results show that SSB does not occur in a real-world (finite
 ) superfluid Bose gas. Therefore\, the phonons in such a gas are not Golds
 tone bosons and are similar to sound in a classical gas\, and the superflu
 idity of such a system is not related to the spontaneous breaking of the $
 U(1)$ symmetry. In the case of an infinite Bose gas\, however\, the situat
 ion becomes paradoxical: the ground state can be regarded as either infini
 tely degenerate or non-degenerate\; this means that the phonon is both sim
 ilar to a Goldstone boson and different from it. [1] \n\n[1] M. Tomchenko\
 , Is a phonon excitation of a superfluid\nBose gas a Goldstone boson? J. P
 hys. A: Math. Theor. 59\, 305202 (2026). https://doi.org/10.1088/1751-8121
 /ae8c94\n\nhttps://indico.bitp.kiev.ua/event/18/contributions/503/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/503/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Propagation of correlations in quantum systems of many particles a
 nd kinetic equations
DTSTART;VALUE=DATE-TIME:20260924T073000Z
DTEND;VALUE=DATE-TIME:20260924T075000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-502@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Viktor Gerasimenko (Institute of mathematics NAS of 
 Ukraine)\nThe talk provides an overview of recent progress in the mathemat
 ical understanding \nof kinetic equations that govern quantum systems with
  many particles.\n\nThe talk will begin by discussing an approach to descr
 ibing the evolution of correlations in systems of many quantum particles. 
 This method is based on the von Neumann hierarchy of evolution equations f
 or a sequence of correlation operators or cumulants of the density operato
 rs. It will be proved that the constructed dynamics of correlations underl
 ie the description of the evolution of the state\, both for finitely and i
 nfinitely many quantum particles\, governed by the BBGKY hierarchy for red
 uced density operators or by the hierarchy of nonlinear evolution equation
 s for reduced correlation operators.\n\nFurthermore\, this discussion will
  demonstrate that the concept of cumulants of the groups of operators for 
 the von Neumann equations underlies nonperturbative solutions to hierarchi
 es of fundamental equations that describe the evolution of observables and
  of the state of many quantum particles\, as well as forming a foundation 
 for the kinetic description of their collective behavior.\n\nThe talk will
  also introduce a new approach to the problem of a rigorous description of
  kinetic evolution using reduced observables. One of the advantages of the
  developed approach to deriving kinetic equations from the underlying dyna
 mics of many particles is the ability to construct kinetic equations that 
 incorporate initial correlations and to describe the processes of propagat
 ing these initial correlations under appropriate scaling approximations.\n
 \n\nReferences\n\n[1] Gerasimenko\, V.I. Hierarchies of quantum evolution 
 equations and dynamics of many-particle correlations\, in: Statistical Mec
 hanics and Random Walks: Principles\, Processes and Applications\, N.Y.: N
 ova Sci. Publ.\, Inc.\, 2013\, 233-288.\n[2] Gerasimenko\, V.I.\, Gapyak\,
  I.V. Cumulant expansions of operator groups of quantum many-particle syst
 ems. Ukrainian Math. J. 78(3-4) 218-234 (2026). doi:10.3842/umzh.v78i3-4.9
 375\n[3] Gerasimenko\, V.I. The Heisenberg picture of quantum kinetic evol
 ution in the mean-field limit. Kinetic & Related Models. 4(1) 385-399 (201
 1). doi:10.3934/krm.2011.4.385\n[4] Gerasimenko V.I.\, Gapyak I.V. Propaga
 tion of correlations in a hard-sphere system. J Stat. Phys. 189(2)\, (2022
 ). doi:10.1007/s10955-022-02958-8\n[5] Gerasimenko\, V.I.\, Gapyak\, I.V. 
 Boltzmann-Grad asymptotic behavior of collisional dynamics. Reviews in Mat
 h. Phys. 33 2130001 32 (2021). doi:10.1142/S0129055X21300016\n\nhttps://in
 dico.bitp.kiev.ua/event/18/contributions/502/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/502/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Seeing Effective Field Theory of Neutron Decay through of Double C
 ategories
DTSTART;VALUE=DATE-TIME:20260923T134000Z
DTEND;VALUE=DATE-TIME:20260923T140000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-500@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Stepan Moskaliuk (Bogoliubov Institute for Theoretic
 al Physics)\nIn this talk the Standard Model of the neutron decay is descr
 ibed by the exchange of the electroweak $W$ boson. However\, energy scales
  for this process ($\\sim \\mathrm{MeV}$) are well below the electroweak s
 cale ($\\sim 100~\\mathrm{GeV}$). Consequently\, the historical descriptio
 n within the low-energy effective field theory (EFT) is the correct physic
 s picture for the neutron decay\, on the one hand. On the other hand\, exp
 ansion of the categorical point of view on many areas of  mathematical phy
 sics will cause to deeper understanding of genuine features of these probl
 ems. New applications of categorical methods are\nconnected with new addit
 ional structures on categories. One of such structures\, a double category
 \, is considered in this talk. The double category structure is defined as
  generalization of the bicategory\nstructure. The use of EFT techniques an
 d category-theoretical methods is not a mere reformulation of the problem.
    Different formulations of EFTs lead to identical mappings of one set  o
 f finite quantities (parameters of the theory) to another set of finite qu
 antities (results of measurements\,  cross-sections\, etc.).  It means tha
 t the presence of infinities (quartic\,  quadratic and etc.) is formalism 
 dependent\, and thus their absence or presence should not be served as an 
 argument for selecting this or that physical theory. This shows that the s
 o-called technical hierarchy problem (the sensitivity of low-energy physic
 s \nto high-energy physics) depends on the formulation of quantum field th
 eory\, and\, therefore\, is devoid of physical meaning\, at least for reno
 rmalisable theories.   The  EFT also provides a rigorous way to connect sc
 ales and estimate uncertainties. Moreover\, EFT methods can  bring new ins
 ights to the problem. In fact\,  by providing a simple framework to analyz
 e hadronic correlation functions\,  the study of neutron decay to $\\mathc
 al{O} (G_F \\alpha)$ in Heavy Baryon Chiral Perturbation Theory (HBChPT) h
 as uncovered a new \\%-level ``inner" correction to the ratio $g_A/g_V$ of
  axial-vector to vector nucleon couplings\, missed in previous analyses ba
 sed on current algebra. The leading-order amplitude for the neutron decay 
 is proportional to the Fermi coupling constant $\\mathrm{G}_\\mathrm{F}$\,
  which is precisely determined from the muon decay. Charged currents with 
 quarks introduce the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $V_{ud
 }$ to the neutron beta decay amplitude. At low energies\, the neutron deca
 y is described by two coupling constants: the vector $g_\\mathrm{V}$ and t
 he axial-vector $g_\\mathrm{A}$. In the reference of this talk\, there are
  presented all theoretical works rely on the precise evaluation of electro
 weak\, quantum chromodynamics (QCD)\, and long-distance hadronic contribut
 ions to these coupling constants. \n  In the HBChPT framework for single-n
 ucleon weak charged-current (CC) processes\, the active degrees of freedom
  are the light leptons\, photons\, pions\, and nucleons. The effect of bot
 h electroweak- and other hadronic-scale physics is encoded in a number of 
 low-energy constants (LECs). The goal of this talk is to develop a matchin
 g procedure  to express the relevant LECs in terms of perturbatively calcu
 lable Wilson coefficients and hadronic correlation functions that can then
  be estimated with  non-perturbative methods\, such as dispersive methods 
 or lattice QCD. Since there are multiple thresholds\, the electroweak scal
 e $\\sim M_{W\,Z}$\, the chiral symmetry breaking scale $\\Lambda_\\chi \\
 sim m_N\\sim$~GeV\, with $m_N$ the mass of nucleon\, and the pion mass\, w
 e adopt a multi-step matching strategy. The first step connects the  Stand
 ard Model EFT to  the  low-energy effective theory (LEFT) below the weak s
 cale\, which coincides with the $V-A$ theory of weak interactions augmente
 d by QED and QCD. This is a perturbative matching step. The second step co
 nnects the double category of  LEFT to the double category of HBChPT by do
 uble category functors and involves non-perturbative physics.  The third s
 tep consists of integrating out the pions\, by matching the double categor
 y of HBChPT onto a  double category of pionless EFT.\n\nhttps://indico.bit
 p.kiev.ua/event/18/contributions/500/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/500/
END:VEVENT
BEGIN:VEVENT
SUMMARY:q and mu extensions of special function in quantum field theory
DTSTART;VALUE=DATE-TIME:20260924T070000Z
DTEND;VALUE=DATE-TIME:20260924T073000Z
DTSTAMP;VALUE=DATE-TIME:20260916T085937Z
UID:indico-contribution-18-497@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Johannes Bluemlein ()\nAnalytic higher order perturb
 ative calculations in quantum field theory lead to special function spaces
  representig the Feynman integrals. We report on the recently obtained  $q
 $- and $\\mu$-extensions of these special function spaces.\n\nhttps://indi
 co.bitp.kiev.ua/event/18/contributions/497/
LOCATION:Bogolyubov Institute for Theoretical Physics Conference Hall
URL:https://indico.bitp.kiev.ua/event/18/contributions/497/
END:VEVENT
END:VCALENDAR