BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Quantum Computing Study of the Speed of Quantum Evolution in the I sing Model in a Longitudinal Magnetic Field DTSTART;VALUE=DATE-TIME:20260922T145000Z DTEND;VALUE=DATE-TIME:20260922T145500Z DTSTAMP;VALUE=DATE-TIME:20260914T032235Z UID:indico-contribution-85-546@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 DTSTART;VALUE=DATE-TIME:20260922T144500Z DTEND;VALUE=DATE-TIME:20260922T145000Z DTSTAMP;VALUE=DATE-TIME:20260914T032235Z UID:indico-contribution-85-556@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 DTSTART;VALUE=DATE-TIME:20260922T144000Z DTEND;VALUE=DATE-TIME:20260922T144500Z DTSTAMP;VALUE=DATE-TIME:20260914T032235Z UID:indico-contribution-85-519@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 DTEND;VALUE=DATE-TIME:20260922T144000Z DTSTAMP;VALUE=DATE-TIME:20260914T032235Z UID:indico-contribution-85-516@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:20260914T032235Z UID:indico-contribution-85-513@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:20260914T032235Z UID:indico-contribution-85-509@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:20260914T032235Z UID:indico-contribution-85-537@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:20260914T032235Z UID:indico-contribution-85-552@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:20260914T032235Z UID:indico-contribution-85-522@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:20260914T032235Z UID:indico-contribution-85-531@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:20260914T032235Z UID:indico-contribution-85-536@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:20260914T032235Z UID:indico-contribution-85-529@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:20260914T032235Z UID:indico-contribution-85-498@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:20260914T032235Z UID:indico-contribution-85-557@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:20260914T032235Z UID:indico-contribution-85-521@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:20260914T032235Z UID:indico-contribution-85-564@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:20260914T032235Z UID:indico-contribution-85-545@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:20260914T032235Z UID:indico-contribution-85-528@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:20260914T032235Z UID:indico-contribution-85-515@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:20260914T032235Z UID:indico-contribution-85-501@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:20260914T032235Z UID:indico-contribution-85-559@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:20260914T032235Z UID:indico-contribution-85-558@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:20260914T032235Z UID:indico-contribution-85-535@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:20260914T032235Z UID:indico-contribution-85-555@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:20260914T032235Z UID:indico-contribution-85-505@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:20260914T032235Z UID:indico-contribution-85-514@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:20260914T032235Z UID:indico-contribution-85-526@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 END:VCALENDAR