SCIENCE BRINGS NATIONS TOGETHER VIII International Conference "Models in Quantum Field Theory"

Oct 6, 2025, 8:00 AM → Oct 10, 2025, 8:00 PM Europe/Moscow

EIMI

The international conference “Models in Quantum Field Theory” (MQFT–2025) will be held in Saint Petersburg, Russia on October 6 – 10 of 2025.

The conference is jointly organized by 

• Saint Petersburg State University;
• Joint Institute for Nuclear Research;
• Leonhard Euler International Mathematical Institute;
• B.P. Konstantinov Petersburg Nuclear Physics Institute of the National Research Centre “Kurchatov Institute”.

The main topics of the conference cover the most actual and important problems related to the construction and investigation of the quantum field theory models across various areas of the modern theoretical physics:

• Mathematical methods in QFT;
• Quantum field theory methods in elementary particle physics;
• Field theoretical methods in statistical physics;
• Gravitation and cosmology;
• Integrable models, symmetries in QFT and quantum groups.

The types of presentations will include plenary talks, session talks and poster session.

Both Russian and English are the official languages of the conference; however, the Organizing Committee kindly requests participants to prepare their slides and posters in English only.

The conference proceedings are planned to be published in a special issue of Theoretical and Mathematical Physics.

The conference is supported by the Ministry of Science and Higher Education of the Russian Federation, agreements 075-15-2025-343, 075-15-2025-344.

Poster Abstracts.pdf

Poster_MQFT_2025.pdf

Mon, October 6

9:00 AM → 10:00 AM Registration

10:00 AM → 11:20 AM Plenary Session

10:00 AM Opening

Speaker: Mikhail Braun (Saint-Petersburg State University)

Braun_MQFT_2025.pdf

10:10 AM Statistical Field Theory Across Classical Nonequilibrium Noise-Driven Systems

Over the past five decades, methods of quantum field theory (QFT) have been fruitfully applied to a broad class of problems in classical physics — including phase transitions, chemical reaction kinetics, percolation, interfacial growth, fully developed turbulence, magnetohydrodynamics, and related phenomena — substantially advancing our understanding of complex stochastic systems and catalyzing the emergence of statistical field theory. For several representative models with distinct physical content, the principal stages of adapting QFT techniques to stochastic problems, highlighting issues associated with the structure of propagators and the selection of noise correlators, are delineated. The main results for fixed points, control parameters, and critical exponents are presented up to three-loop order.

Speaker: Michal Hnatic (JINR,BLTP)

Hnatic PETERBURG_2025.pdf

10:45 AM Multipurpose Renormalization Group as a consequence of locality of QFT

R-operation and locality of QFT guarantees locality of the counterterms in coordinate space or at most polinomiality in momentum space. This leads to relations between the counterterms in subsequent orders of perturbation theory. In its turn these relations allow one to get the recurrent relations which can be promoted to RG equations for the leading, subleading, etc logarithms. Remarkably that the RG equations in sub, subsub, etc orders are always linear differential ones.
The advocated formalism works equally well in renormalizable and non-renormalizable theories.
Different examples are presented.

Speaker: Dmitry Kazakov (JINR)

Kazakov StP25.pdf

11:20 AM → 11:40 AM Coffee

11:40 AM → 1:15 PM Plenary Session

11:40 AM A Brief History of the AdS/CFT Correspondence and the Holographic Approach to Strong Interactions

The talk will briefly cover the history of the emergence of the AdS/CFT correspondence (also called gauge-gravity or holographic duality) in string theory, as well as the subsequent application of the emerged ideas to the description of the phenomenology of non-perturbative strong interactions.

Speaker: Sergey Afonin (Saint Petersburg State University)

MQFT2025.pdf

12:20 PM Holographic QCD and Critical Phenomena at the Phase Transition

We investigate critical behavior near first-order phase transitions in QCD using gauge/gravity duality. A key focus is the selection of holographic models that best predict the locations of these transitions, including via modern machine learning methods. We also present new results on anisotropic holographic QCD, highlighting the non-trivial behavior of key equation-of-state parameters under anisotropy.

Speaker: Irina Aref'eva (Steklov Mathematical Institute)

arefeva-MQFT2025.pdf

1:00 PM Group Photo

1:15 PM → 2:30 PM Lunch

2:30 PM → 4:30 PM Section A: Mathematical methods in QFT

2:30 PM Continuous spin superparticle models

New continuous spin superparticle models in 4D, N=1 flat and AdS_4 superspace are presented. The models are described by 4D, N=1 superspace coordinates together with commuting Weyl spinor additional variables, which are inherent ingredients of continuous spin models. A canonical formulation, specific local fermionic kappa-symmetry, and a compete system of bosonic and fermionic constraints are derived. All bosonic constrains are first-class, while four fermionic constraints are a mixture of first and second classes. It is proved that in the flat case two constraints are the first-class and two constraints are the second-class, whereas in curve case only one fermionic constraint is a first-class constraint, while the other three are second-class constraints. Using additional variables inherent in to the model, we split the fermionic constraints into first and second classes in a covariant way. Quantization of the model in flat case is carried out according to the Gupta-Bleuler procedure. The corresponding wave function, which is either a chiral or antichiral superfield, depends on additional variables and obeys the superfield constraints that define the continuous spin irreducible representation of the Poincaré supergroup in the superspace.

Speaker: Sergey Fedoruk (BLTP JINR)

Fedoruk-MQFT'25.pdf

3:00 PM On the inconsistency of supersymmetric wess-Zumino model

We prove that the supersymmetrcic Wess-Zumino model is internally incosistent as a local quantum field theory model.

Speaker: Nikolai Krasnikov (Institute for Nuclear Research RAS)

MQFT_Krasnikov.pdf

3:30 PM Discrete spectrum of edge states in a two-dimensional topological insulator

The interaction model of two electrons in the edge states of a two-dimensional topological insulator is investigated. Both solutions of the Schr\"odinger equation and solutions of the Bethe-Salpeter equation at different values of the Fermi energy are considered. It is shown that for the Bethe-Salpeter equation, which takes into account the existence of the Fermi surface, there is a discrete spectrum in the system of two electrons. This phenomenon does not appear in the case of the Schr\"odinger equation.

Speaker: Ivan Terekhov (ITMO University)

Terekhov2025.pdf

4:00 PM Chaos in non-equilibrium quantum field theory and holography

In this talk (based on arXiv 2507.18746 and 2507.22999) I will show that in a massive scalar theory on a finite cylinder, operator local perturbations(quenches) drive dynamics whose time-resolved two-point functions exhibit spacing-ratio statistics along with other measures showing clear random-matrix behaviour. Extending to holography, I construct confining deformations by capping off AdS (and BTZ) with a hard wall and derive exact Green’s functions for post-quench evolution. In these confining backgrounds, fluctuations of boundary observables approach Wigner–Dyson behavior, with chaotic signatures amplified for heavier operators and for walls placed closer to the boundary.

Speaker: Dmitry Ageev (Steklov Mathematical Institute, RAS)

Petersburg_Talk_2025.pdf

2:30 PM → 4:30 PM Section B: Quantum field theory methods in elementary particle physics

2:30 PM Generation of a scalar vortex in {a} rotational frame

The interplay of rotation, external magnetic fields, and quantum fields has become an active topic at the interface of quantum field theory, condensed matter, and high-energy physics. In this contribution, we study the formation of scalar condensates in a rotating frame and, in particular, the emergence of vortex solutions in a charged scalar field. Our analysis is motivated both by fundamental interest in vacuum instabilities under extreme conditions and by possible applications to systems such as pion condensation in heavy-ion collisions or other strongly interacting media where rotation and magnetic flux may play a decisive role.

We build upon earlier work that demonstrated vacuum Bose condensation of a charged scalar field inside a uniformly rotating cylindrical system subjected to an all-pervading uniform magnetic field with Dirichlet boundary conditions. In the present study, we extend this setting to include a configuration where the magnetic field is confined to a thin flux tube aligned with the cylinder’s axis, rather than filling the entire volume. This geometry allows us to study the influence of the shape of the magnetic field.

The dynamics of the condensate are described by the nonlinear Ginzburg–Pitaevskii equation, which we solve perturbatively, numerically and using a semi-analytical approach for a range of parameters. We determine the critical angular velocities required for the onset of condensation, the spatial distribution of the scalar field, the average radii of the condensate, and the associated energies. We confirm the validity of the perturbative approach close to the onset of condensation. We show how for a rather strong condensate, its profile function shows a plateau.

A key finding is that, for the same external parameters, the energy of the condensate in the flux-tube configuration is significantly lower than that in the uniform magnetic-field case. This result suggests that localized flux tubes provide a more energetically favorable environment for vortex formation and scalar condensation. From a broader perspective, this observation indicates that the structure of the external magnetic field—whether extended or localized—can crucially influence both the stability and morphology of scalar condensates in rotating systems.

Beyond its theoretical significance, this study highlights possible implications for physical systems where rotation and magnetic fields coexist. In particular, the results may provide insights into the behavior of pion fields in the vortical and magnetized environments generated during relativistic heavy-ion collisions, where similar mechanisms could govern the emergence of novel collective states. More generally, the framework developed here contributes further to a bridge between condensed-matter analogues of vortex formation, such as in superconductors or superfluids, and high-energy scenarios where rotation and quantum fields intersect.

Speaker: Michael Bordag (Universität Leipzig)

TalkBordag.pdf

3:00 PM Chiral Approach to Massive Higher Spins

Effective field theory of composite higher-spin particles is a formidable subject, where preserving the physical number of degrees of freedom in a Lorentz-invariant and parity-even way requires a host of auxiliary fields. They can be chosen to have a rich gauge-symmetry structure, but introducing consistent interactions in such approaches used to be a highly non-trivial task, with Lagrangians usually specified only up to three points. In this talk, I will discuss a new chiral-field description for massive higher-spin particles, which in four spacetime dimensions allows to do away with the unphysical degrees of freedom. This greatly facilitates the introduction of consistent interactions. I will focus on three theories, in which higher-spin matter is coupled to electrodynamics, non-Abelian gauge theory or gravity. These theories are the first toy models for consistently interacting massive higher-spin fields at any multiplicity.

Speaker: Alexander Ochirov (ShanghaiTech)

MQFT2025.pdf

3:30 PM Exact High-Multiplicity Amplitudes from Landau Method

Inspired by quantum-mechanical Landau method, we propose a new perturbatively exact relation between scattering amplitudes in bosonic theories and vacuum-to-vacuum transition amplitudes in the same theories with vanishingly weak sources on singular backgrounds. We argue that the new relation automatically resums the powers of gn in perturbative amplitudes of n quanta production, where g is a coupling constant. In this way, one can describes double-scaling limits g->0, gn=const of n-particle production in quantum field theory and of vacuum-to-nth excited state transitions in quantum mechanics. In the lowest semiclassical order, our relation reproduces D.T. Son's method of singular solutions and proves Rubakov-Son-Tinyakov conjecture. We illustrate it in the model of anharmonic oscillator and discuss its application to multiparticle production in the scalar lambda phi^4 theory.

Speaker: Dmitry Levkov (INR RAS & ITMP MSU)

levkov-mqft2025.pdf

4:00 PM Lepton flavor violation induced by the curved field space

In this talk, I represent a scenario where the nonzero curvature extension of the field space for the charged leptons induces a peculiar force that leads to a simple mechanism for generating the charged lepton flavor violation (CLFV). This novel force corrects the electromagnetic vertex, leading to an effective coupling which is flavor off-diagonal at tree level. Consequently, it yields the CLFV decays with the very strongly enhanced sensitivity, allowing for probes in the regime of tiny CLFV coupling, which is out of reach of the previous models.

Speaker: Cao Hoang Nam

CHNam-MQFT2025.pdf

2:30 PM → 4:30 PM Section C: Field theoretical methods in statistical physics

2:30 PM Skyrmion crystals and thermal Hall effect

Magnetic skyrmions at the scale of tens of nanometers are actively discussed in the last decade. These topological objects are experimentally observed as skyrmion crystals (SkX) in a tightly packed triangular configuration. The main focus of experimental investigations and numerical modeling nowadays shifts to the preparation and manipulation of individual skyrmions, aiming to use them in future electronic devices. The dynamics or heat transport properties of regularly arranged SkX, attract less attention.

Using the method of stereographic projection, we map the vector field of local magnetization to the complex-valued field. The static configuration of SkX is described by a simple trial function, with optimal parameters found numerically. The dynamics is then determined by considering the second variation of the action and eventual semi-classical quantization. The calculation of the spectra shows that several magnon branches have non-trivial topology and non-zero Chern numbers. [1] The topological character of low-energy magnon branches may change upon variation of external magnetic field. [2] We argue that the latter topological transition in magnon spectra should be visible in thermal Hall effect at low temperatures.

[1] V. E. Timofeev and D. N. Aristov, Phys. Rev. B 105, 024422 (2022).

[2] V. E. Timofeev and D. N. Aristov, JETP Lett. 117, 9 (2023); ibid. 118, 448 (2023); V. E. Timofeev, Yu. V. Baramygina, and D. N. Aristov, JETP Lett. 118, 911 (2023).

Speaker: Dmitry Aristov (PNPI - NRC Kurchatov Institute)

Aristov_MQFT_2025.pdf

3:00 PM Magnon edge modes of skyrmion crystal in nonuniform magnetic field

Magnetic skyrmions are topologically nontrivial whirls of local magnetization, that can arrange into regular lattices, co-called skyrmion crystals (SkX). Dzyaloshinskii-Moriya interaction (DMI) is one of SkX stabilization mechanisms. There is a wide region on a phase diagram of a thin ferromagnetic film with DMI in a presence of an external magnetic field where SkX is a ground state of the system [1]. Whirling character of the ground state leads to a complicated band structure of SkX excitations. Besides the topologically trivial Goldstone mode, other low-energy bands may also possess non-zero Chern numbers. Recently it was theoretically shown that there is a topological transition in the spectrum of SkX excitations: gap between two low-lying bands closes with increasing of magnetic field, and after that gap reopens and Chern numbers are changed [2,3].

We investigate appearance of edge modes in a system with a nonuniform external magnetic field. We consider two half-planes with different values of external magnetic field: below topological transition and above it. We show that there is a chiral magnon edge mode in this system, localized on a border of these two areas. We compare two different approaches: numerical analysis of the full spectrum of excitations [4] and analysis of the reduced effective model developed earlier [3]. Character of wave functions is discussed; localization length dependence of model parameters is obtained.

[1] N. Nagaosa and Y. Tokura, Nature Nanotechnology 8, 899 (2013).
[2] S. A. Diaz, T. Hirosawa, J. Klinovaja, and D. Loss, Physical Review Research 2, 013231 (2020).
[3] V. E. Timofeev, Yu. V. Baramygina, D. N. Aristov, JETP Letters, 118, 12, 911-916, (2023).
[4] V. E. Timofeev and D. N. Aristov, Phys. Rev. B 105, 024422 (2022).

Speaker: Viktor Timofeev (NRC "Kurchatov Institute", Petersburg Nuclear Physics Institute)

Timofeev_MQFT_06.10.25.pdf

3:30 PM Fluctuation-Driven Phase Transitions in SU(N) Fermi Gases: A Functional RG Perspective

We explore superfluidity in $SU(N)$ Fermi gases using the functional renormalization group. Going beyond mean-field we track the flow of the effective action and resolve thermodynamics near the transition. Our study uncovers a fluctuation-induced first-order superfluid transition for $N \geq 4$, absent at mean-field level. We quantify the critical temperature and the discontinuities in the gap and entropy density, showing that increasing $N$ lowers $T_c$ but amplifies the sharpness of the transition

Speaker: Georgii Kalagov (BLTP JINR)

MQFT_Kalagov.pdf

4:00 PM Equation of state for directed percolation: Three-loop approximation

In this work, we employ a field-theoretic renormalization group approach to study a paradigmatic model of directed percolation. We focus on the perturbative calculation of the equation of state, extending the analysis to the three-loop order in the expansion parameter $\varepsilon = 4-d$. The main aims of this study are to provide an update on this ongoing work and to present the numerical technique developed for the necessary calculations. We verify existing two-loop results and enumerate the complete set of Feynman diagrams necessary for the three-loop calculation.

Speaker: Lukas Mizisin (BLTP, JINR)

Mizisin_MQFT_2025.pdf

4:30 PM → 5:00 PM Coffee

5:00 PM → 6:20 PM Section A: Mathematical methods in QFT

5:00 PM Holographic vacuum misalignment

In this talk, I present a bottom-up holographic model dual to a strongly coupled field theory which incorporates the spontaneous breaking of an approximate global symmetry yielding the SO(5)/SO(4) coset important for minimal composite-Higgs models. The gravity solution is smooth, mimicking confinement on the field theory side. A set of boundary terms are added to the gravity, introducing additional symmetry-breaking effects, that capture the results of coupling the dual field theory to a weakly coupled sector. This results in breaking the SO(4) to an SO(3) subgroup via vacuum misalignment as a toy model for the electroweak symmetry breaking. We compute the spectrum of fluctuations of the model, focusing on the Higgs-like excitations and comparing their mass to heavier modes.

Based on 2405.08714.

Speaker: Ali Fatemiabhari (ITMP, Moscow)

presentationSt.pdf

5:20 PM Holographic RG flows in a 3D gauged supergravity

We focus on the study of RG flows of conformal field theories that are holographically dual to Poincare domain wall solutions in $D=3$, $N=(2,0)$ gauged supergravity coupled to a sigma model with target spaces $S^2$ or $\mathbb{H}^2$. This theory is truncated to a subsector where the vector field and phase of the scalar field vanish and we consider dynamics of the remaining real scalar field. The RG flows, which are mostly non-superysymmetric, are analyzed by treating the supergravity field equations as a dynamical system for the scalar field and its derivative with respect to the scale factor. Phase diagrams are constructed for different values of the parameter $a^2$, which is related to the curvature of the scalar manifold. Obtained RG flows are interpreted using the holographic dictionary. For the case of $S^2$ target space we also provide and interpretate thermal flows as a special gravitational solutions. During the talk we consider exotic RG flows and give some hints to understand their nature.

Speaker: Lev Astrakhantsev (BLTP JINR, MIPT)

RG_Flows_MQFT_25.pdf

5:40 PM Geometric approaches for constructing supergravity solutions in holography context

In experimental science, many phenomena remain beyond a self-consistent theoretical description. A prominent example is provided by the strong interaction: Yang–Mills theory, which models it, requires solving highly nonlinear equations that are still intractable in general. Several decades ago, however, advances in string theory led to the holographic correspondence (AdS/CFT). By analyzing the equations of motion of supergravity---the low-energy limit of string theory—in the classical supergravity regime, one can extract correlation functions of the dual conformal field theory at strong coupling. For instance, linearized perturbations around the $AdS_5\times S^5$ background allow one to compute correlators of $\mathcal N=4 \ SYM$ in the strong-coupling limit. Although the underlying theories remain strongly nonlinear, this framework reduces many otherwise formidable correlation-function calculations to solving differential equations for small supergravity perturbations, which are often tractable analytically or, at least, numerically. Consequently, further developing both holographic methods and techniques for solving supergravity equations is crucial for a more refined description of strong-interaction and nuclear phenomena, with the potential to yield new discoveries.
One of ways for generating new supergravity solutions is to study the solution space as a geometric object endowed with hidden symmetries, the best-studied of which is T-duality. In this context, a useful operation is the so-called $\beta$ -- deformation, encapsulated by
\begin{equation}
\bigl( (g+B)^{-1}+\beta \bigr)^{-1} = G+B ,
\end{equation}
where $g$ and $B$ are the metric and Kalb–Ramond two-form of a given bosonic supergravity background, $\beta$ is a bivector chosen along isometries of the background, and $G$ and $B$ denote the fields of the deformed solution. This construction exploits the fact that ten-dimensional supergravity arises as the low-energy effective theory of strings, which possess duality symmetries; at low energies these appear as families of solutions generated from highly symmetric seeds. The deformation is constrained by
\begin{equation}
\beta = \rho^{ab}\, k_a \wedge k_b,\qquad \rho^{a[b}\,\rho^{|c|d}\, f_{ac}{}^{e]}=0,
\end{equation}
where $k_a$ are Killing vectors, $\rho^{ab}$ encodes the bivector deformation along these isometries, and $f$are the structure constants defined by $[k_a,k_c]=f_{ac}{}^{e} k_e$.
For deformations produced in this way, a holographic interpretation can be formulated. Particularly interesting results arise when the Killing vectors generate a compact abelian Lie algebra: the image on the gauge-theory side is a manifold of conformal fixed points. By contrast, the (homogeneous) classical Yang–Baxter equation (CYBE) severely constrains—indeed forbids compact non-abelian bivector deformations, which limits strong this solution-generating method.
However, T-duality is not the only hidden symmetry inherited from string theory. U-duality, a richer symmetry of string theory, also has a supergravity representation and admits an analogue of the bivector construction in terms of polyvector deformations. It has been shown that certain tri- and quadrivector deformations generate new solutions of eleven-dimensional and type IIB supergravity. Moreover, there is no theorems or geometrical reasons to expect impossibility of using of compact non-abelian bivector deformations in the polyvector case. A natural objective, therefore, is to formulate an appropriate generalization of the CYBE that fully characterizes admissible three- and four-vector deformations, in parallel with the bivector theory, which is current task of my work.

Speaker: Timophey Petrov (MIPT, ITMP MSU)

petrovmqft.pdf

6:00 PM De Sitter entropy: on-shell versus off-shell

Attributing thermodynamic properties to the Bunch-Davies state in static patch of de Sitter space and setting the corresponding equations of state, we demonstrate that, for pure gravity, the bulk entropy computed on-shell as a volume integral in de Sitter space coincides with the Wald entropy (area law) in any spacetime dimension and for any theory of f(R) gravity. We extend this result to the renormalized entanglement entropy of a non-minimally coupled scalar field. From the on-shell perspective, entropy emerges as a bulk contribution, whereas from the off-shell viewpoint, it manifests as a boundary (horizon) contribution. As a result, in de Sitter space, generalized entropy can be understood in two distinct ways: either as a bulk or as a boundary contribution

Speaker: Dmitrii Diakonov (MIPT and ITEP)

ds_thermodynamics (2).pdf

5:00 PM → 6:20 PM Section C: Field theoretical methods in statistical physics

5:00 PM High Energy Behavior of the 4-fermion interaction

We consider the $f f \rightarrow f f$ scattering amplitudes for the a massless four-fermion interaction model in four dimensions. At first we take the simplest version with the scalar current-current interaction. The loop corrections up to the three-loop level are calculated within the spinor-helicity formalism using the Weyl spinors. We find out that there are two independent spinor structures that appear in all orders of perturbation theory that can be separated when calculating the diagrams. Our aim is to calculate the leading divergences within the dimensional regularization. To check the validity of our calculations, we use the recurrence relations that connect the leading divergences in the subsequent orders of perturbation theory. Then we can provide the resummation procedure of the leading divergencies in all loop orders, to study the high energy behavior of the theory. At the end we will consider the physically more interesting case of V-A interaction.

Speaker: Arthur Borlakov (JINR)

Borlakov_MQFT.pdf

5:20 PM Three-loop singularity structure of a principal chiral field model

The talk is devoted to the three-loop renormalization of the effective action for a two-dimensional pricipal chiral field model using the background field method and a cutoff regularization in the coordinate representation. The coefficients of the renormalization constant and the necessary auxiliary vertices are found. Asymptotic expansions for all three-loop diagrams and their dependence on the type of regularization function are also studied.

Speaker: Pavel Akacevich (PDMI RAS)

Akacevic_mqft.pdf

5:40 PM Two-Loop Renormalization of Stochastic Magnetohydrodynamics: Field-Theoretic Results

We study a stochastic version of magnetohydrodynamics (MHD) formulated as the generalized A-model of a passively advected vector field with full back-reaction on the flow. The model includes parity breaking via a helicity parameter ρ and a continuous interaction parameter A that interpolates between important physical limits (A = 1 for MHD, A = 0 for passive vector advection). Using the field-theoretic renormalization-group approach and the ε-expansion, we perform a two-loop calculation of the renormalization constants that govern the magnetic-field sector and focus in particular on the three-point vertex $Γ_{v′bb}$ and the associated constant $Z_3$. The one-loop structure is recovered and extended to arbitrary A, while the two-loop pole structure is evaluated numerically. For the physically relevant three-dimensional MHD case (A = 1) we obtain an explicit two-loop contribution to the magnetic anomalous dimension which depends on helicity as $c_{2,1}^{A=1} = C(3) [0.201432 + ρ²·0.288499]$ (with $C(3)=1/(480π⁴)$), demonstrating a nontrivial $\rho^2$ dependence at this order. These results advance multiloop RG treatments of dynamo-type effects and provide groundwork for future studies of scaling and anomalous exponents in helical MHD turbulence.

Speaker: Iurii Molotkov (JINR)

Molotkov_mqft.pdf

6:00 PM Two-loop turbulent helical magnetohydrodynamics: Large-scale dynamo and energy spectrum

We performed a two-loop field-theoretic analysis of incompressible, helical magnetohydrodynamics (MHD) in a fully developed, statistically stationary turbulent state. A distinctive feature of turbulence in helical media is the emergence, within the loop expansion of the magnetic response function, of an infrared-relevant, mass-like contribution. Physically, this term corresponds to a perturbation of the Joule dissipation proportional to the current helicity, ${\bf \nabla}\times{\bf b}$ (with ${\bf b}$ the magnetic field), and its presence destabilizes the trivial vacuum $\langle {\bf b} \rangle = 0$, thereby rendering the entire system unstable. We identify two stabilization mechanisms: (i) the induction equation governing the magnetic field can be augmented by an external mass-like parameter that exactly cancels the dangerous loop correction, thereby defining a kinematic regime; (ii) alternatively, the system may undergo spontaneous breaking of rotational symmetry, selecting a new vacuum endowed with a nonvanishing large-scale mean field $\langle {\bf b} \rangle = {\bf B}$—a turbulent dynamo regime. Physically, the (large-scale) dynamo regime is the state that typically emerges in MHD systems after sufficient time. By contrast, the kinematic regime provides an approximation valid when the emergent ${\bf B}$ remains relatively small. Our study focuses primarily on the dynamo regime, which is widely understood to underlie the generation of magnetic fields in astrophysical objects. We demonstrate that the emergence of an anomalous mean magnetic field is sufficient to stabilize the system, and we provide a two-loop determination of its amplitude. Our analysis shows that the appearance of ${\bf B}$ induces Goldstone-type modifications of the Alfvén modes and generates additional anisotropic structures. For turbulent spectra in the dynamo regime, we compute the two-loop contribution to the magnetic-field anomalous dimension $\gamma_b$. We find that the emergent mean field steepens the magnetic-energy spectrum to $\sim k^{-11/3+2\gamma_{b\star}}$ (with $\gamma_{b\star}=-0.1039-0.4202,\rho^2$ for $|\rho|\le 1$, where $\rho$ quantifies helicity and $\gamma_{b\star}$ denotes $\gamma_b$ evaluated at the Kolmogorov fixed point), in contrast to the Kolmogorov velocity spectrum $\sim k^{-11/3}$; hence the equipartition characteristic of the kinematic regime is violated. Moreover, the dependence of $\gamma_b$ on the mirror-symmetry-breaking parameter $\rho$—which first appears only at two loops—reveals an exceptionally strong sensitivity of the energy cascade to the degree of helicity.

Speaker: Andrei Ovsiannikov

Ovsiannikov_MQFT2025.pdf

5:00 PM → 6:20 PM Section D: Gravitation and cosmology

5:00 PM AdS Radiation and The Flat Limit

Studying the flat limit of AdS/CFT is an important task that aims to make contact with flat-space scattering, BMS symmetries, and ultimately the physics of our universe. A particularly interesting low-energy corner of the holographic principle is the fluid/gravity correspondnce which connects the dynamics of long-wavelength perturbations in AdS space to the one of a relativistic conformal boundary fluid. In this talk, we will consider radiative spacetimes in the context of the fluid/gravity dictionary and consider its flat limit that allow us to describe nontrivial Carrollian conformal fluids and out-of-equilibrium conformal physics.

Speaker: Felipe Diaz (ITMP)

Pres San Pete_rotated_organized (2).pdf

5:20 PM Polynomial supersymmetry for Matrix Hamiltonians and reducibility of matrix intertwining operators.

We consider different types of reducibility of a matrix $n\times n$ intertwining operator and reveal criterion for regular reducibility. It is shown that in contrast to the scalar case $n = 1$ there are for any $n\geqslant 2$ regularly absolutely irreducible matrix intertwining operators of any order $N\geqslant 2$, i.e. operators which cannot be factorized into a product of a matrix intertwining operators of lower orders even with a pole singularity(-ies) into coefficients.

Speaker: Andrey Sokolov (Military Academy of the Signal Corps)

Sokolov - MQFT 2025.pdf

5:40 PM Yang-Baxter structure of the extended space

We construct an analogue of Yang--Baxter deformations defined by a single Killing vector, that is a solution generating transformation in Einstein--Maxwell dilaton theory. We show that these are nothing but a coordinate transformation in a parent theory related to EMd theory by KK reduction. Similarly (almost-abelian) bi-vector Yang--Baxter deformations are coordinate transformations in the doubled space.

Speaker: Kirill Gubarev (MIPT)

Talk_MQFT_2025__SPB_.pdf

6:00 PM Quantum quench in curved space-time

Quench is an abrupt change in a system's parameters. In the quantum context, it can be viewed as a perturbation of the initial state of a quantum field theory relative to a known density matrix, such as that for the vacuum state or a finite-temperature state. Within the framework of the inflationary model of the early universe, a quantum quench can be used to study the system's evolution following a sudden transition during inflation, whose characteristic timescale is much shorter than that of all other processes. As an example, we consider a scalar quantum field theory in de Sitter space to model inflation, examining the expanding Poincaré patch and global de Sitter separately; the latter is characterized by an initial contracting phase. In this setting, we investigate and compare the evolution of the two-point correlator following two types of global quench: first, through an explicit, abrupt change of the scalar field's mass $M\rightarrow m$, and second, via a strong perturbation of the equilibrium density matrix $\widehat{\rho}_0$ by the action of a quench operator $\widehat{Q}$ as $\widehat{\rho} = \widehat{Q}^{\dagger}\widehat{\rho}_0 \widehat{Q}$. The first approach is well-studied in the literature for flat space-time, with several works also existing in a cosmological context. For the second case, the problem of determining the evolution is solved for a specific class of states known as Calabrese-Cardy states. We describe a new class of states where the operator $\widehat{Q}$ inserts, at a specific time $t_0$, an operator polynomial in the scalar field operator $\widehat{\phi}$ into the system's Hamiltonian. We explain how to find the evolution of correlators for such operators using the non-equilibrium Keldysh functional integral formalism. Furthermore, using the simplest example of inserting a quadratic operator, we compare the results for different types of quantum quenches in de Sitter space.

Speaker: Damir Sadekov (MIPT)

quench_in_dS_presentation (1).pdf

6:30 PM → 9:00 PM Welcome Party and Poster Session

Tue, October 7

10:00 AM → 11:20 AM Plenary Session

10:00 AM Standard Model Effective Field Theory (SMEFT)

Due to the lack of statistically reliable manifestations of effects beyond the Standard Model (SM) in LHC experiments, special attention is paid to the construction of an effective field theory in which deviations from the SM are parameterized by a set of gauge-invariant local operators with dimensions greater than four. The main features and current status of this approach, called the Standard Model of Effective Field Theory (SMEFT), are briefly discussed

Speaker: Eduard Boos (SINP MSU)

SMEFT_StPetersburg.pdf

10:40 AM Adjustment of Faddeev-Popov quantization scheme for first stage reducible gauge theories

The method is developed that adjusts the Faddeev-Popov factorization procedure for the quantization of generic reducible gauge theories with linearly dependent generators. Using this method a covariant quantization of recently proposed totally antisymmetric tensor spinor field theory in AdS space is carried out and the corresponding effective action is obtained in terms of special Dirac-type differential operators.

Speaker: Ioseph Buchbinder (Laboratory of Theoretical Physics, Joint Institute for Nuclear Research)

MQFT_2025_Buchinder.pdf

11:20 AM → 11:40 AM Coffee

11:40 AM → 1:00 PM Plenary Session

11:40 AM Gravitational wave probes of the phase transition dynamics in the early Universe: the case of domain walls

Standard Model is neither phenomenologically nor theoretically complete theory of fundamental physics. Many of its motivated extensions predict phase transitions in the early Universe, which, if source the gravitational wave production, may be probed with present and future instruments aimed at measurement of gravitational waves. This is a unique way to trace the history of the early Universe before the Big Bang Nucleosynthesis and search for the new physics at energy scales far above the scale we explore and plan to explore at the Large Hadron Collider and its feasible successors. The statement will be illustrated with an example of simple scalar dark matter and phase transitions accompanied by the domain wall production. The domain wall network generates the gravitational waves, which spectrum (if measured) can tell us about the birth, evolution and death of the network and hence can pin down the new physics parameters responsible for the phase transition and dark matter production. We will describe in detail the network evolution with various initial conditions and for a set of mechanisms destroying this dangerous for cosmology structure.

Speaker: Dmitry Gorbunov (Institute for NUclear Research of the Russian Academy of sciences)

MQFT-2025.pdf

12:20 PM Dimensional transmutation and nonconventional scaling behaviour in a model of self-organized criticality

In this talk we understand by "dimensional transmutation" a situation when, in a certain field theoretic model, a certain canonically dimensionless parameter (like a coupling constant) acquires a nontrival critical dimension in the infrared asymptotic range of scales (long times, large distances). This situation is not unfrequent and was encountered in stochastic magnetic hydrodynamics, turbulent advection of chemically active agent, kinetic roughening of growing surfaces and so on.

Another kind of dimensional transmutation is the situation when a weakly anisotropic model becomes strongly anisotropic in a certain asymptotic regime, corresponding to a certain exceptional fixed point of the renormalization group equation. It is illustrated by the example of strongly anisotropic Hwa-Kardar model of self-organized criticality ("running sandpile" ) coupled with an isotropic environment, described by a certain statistical velocity ensemble for an incompressible fluid.

The original stochastic Hwa-Kardar equation allows for independent scaling of spatial coordinates, the coordinate along the preferred dimension and the coordinates in the orthogonal subspace. This strongly anisotropic behaviour is ruined once the isotropic velocity ensemble is added. However, it is restored in a special asymptotic regime in which the interaction with the environment becomes irrelevant. The mechanism behind this restoration is also based on a specific type of dimensional transmutation.

N.V. A., N.M. Gulitskiy, P. I. Kakin, M.N. Semeikin "Dimensional transmutation and nonconventional scaling behaviour in a model of self-organized criticality" Int. J. Mod. Phys. A37, 2240022 (2022)

N. V. A., N.M. Gulitskiy, P. I.Kakin, G.E.Kochnev "Effects of turbulent environment on self-organized critical behaviour: Isotropy vs anisotropy" Universe 6, 145 (2020)

Speaker: Nikolai Antonov (Saint Petersburg State University, Department of Physics and Joint Institute for Nuclear Research, Bogoliubov Laboratory of Theoretical Physics)

MQFT_Antonov.pdf

1:00 PM → 2:30 PM Lunch

2:30 PM → 4:30 PM Section B: Quantum field theory methods in elementary particle physics

2:30 PM Analizing leptonic decays of heavy quarkonia in the light of the search for New Physics

The leptonic decays of heavy quarkonia are complementary observables to the semileptonic decays of heavy mesons and provide additional insight into the possible lepton flavor universality breaking. These decays are analyzed in the framework of the covariant confined quark model by using a novel approach for the description of the radially excited quarkonia states. It turns out that the experimental data can be described by our approach within the Standard Model without introducing the new physics operators.

Speaker: Mikhail Ivanov (Joint Institute for Nuclear Research, Dubna, Russia)

M.A.Ivanov_MQFT-2025.pdf

3:00 PM Naturalness domain in the Standard Model

The Brout-Englert-Higgs (BEH) boson mass evolution in the Standard Model is discussed. The quadratic self-energy divergence in addition to the logarithmic ones due to the renormalization of the scalar BEH boson mass causes the so-called Naturalness problem.

Speaker: Victor Kim (NRC KI - PNPI, Gatchina)

kim_mqft_2025.pdf

3:30 PM Space-like pion off-shell form factors in the Bethe-Salpeter approach

In the report, the off-shell electromagnetic pion form factors in the Bethe-Salpeter formalism are considered. The separable kernel of the first rank quark-antiquark interaction is used to solve the equation analytically. The half-off-shell pion form factors and, which are related to each other by the Ward-Takahashi identity, are calculated. The obtained off-shell form factors as well as static properties of the pion are compared with the results of other authors

Speaker: Serge Bondarenko (BLTP JINR)

Bondarenko-MQFT-2025.pdf

4:00 PM The rare events at fixed target experiments

The connection between Standard Model (SM) particles and light dark matter (DM) can be introduced via spin-0, spin-1, and spin-2 mediators. Moreover, in a mediator mass range from sub-MeV to sub-GeV, fixed-target facilities such as NA64e, LDMX, E137, NA64mu, and M3 can potentially probe such particles of the hidden sector via missing energy signatures that are described by the bremsstrahlung-like process involving leptons. We discuss current and prospect experimental reaches for hidden mediators in the light of regarding fixed-target experiments. In addition for NA64mu and LDMX we address the prospect sensitivity to millicharged particles, that can be associated with DM fraction.

Speaker: Dmitry Kirpichnikov (INR RAS)

Kirpichnikov_MQFT2025_Oct_07_2025-1.pdf

2:30 PM → 4:30 PM Section C: Field theoretical methods in statistical physics

2:30 PM Hydrodynamics of a Quantum Fluid: The Critical Dimension of Viscosity

The study of critical dynamics in the vicinity of the superfluid phase transition presents an unresolved problem: determining the power-law behavior of viscosity upon approaching the critical point. The corresponding dynamic critical exponent remains unknown. Within a phenomenological model, direct computations prove exceedingly complex; the renormalization procedure involves the mixing of nearly 50 composite operators, leading even to an incorrect sign for the exponent in first-order perturbation theory.

We will discuss how to derive a microscopically justified hydrodynamic equation starting from a quantum field theory model. As a useful benefit, it will be demonstrated that this framework provides an alternative, more streamlined method for computing the critical viscosity.

Speaker: Marina Komarova (Saint Petersburg State University)

talk-eng.pdf

talk-rus.pdf

vasilyev-25.pdf

3:00 PM Hwa–Kardar model of self-organized criticality: Its conceptual significance and behavior in various randomly moving environments

Hwa–Kardar "running' sandpile model was an attempt to construct a continuous stochastic equation (an effective coarse-grained large-scale description), the derivation of which is based solely on conservation laws, relevant symmetries and dimensionality considerations, in order to capture the hypothetical mechanism behind self-organized criticality, namely, transport in a driven diffusive system with anisotropy and conservation. While the model does not include one of the important features of self-organized criticality – separation of time scales – and cannot adequately differentiate between discrete sandpile models, it allows to apply the well-developed methods of quantum field theory to the problem of self-organized criticality.

The very popular concept of self-organized criticality was initially based on specially designed discrete models; now it is considered one of the strongest contenders for the mechanism behind emergent complexity in Nature as it might explain self-similar spatio-temporal correlations in the infrared (large distances, long times) range believed to be observed in a startlingly big number of systems.

In this talk, asymptotic behaviour of a self-organized critical system subjected to a number of different moving random environments is analyzed using field theoretic renormalization group approach. The system is described by the anisotropic continuous Hwa–Kardar model while the medium is described by "synthetic" Gaussian ensembles due to Kraichnan and Avellaneda–Majda and their generalizations (general spatial dimension $d$ and finite correlation time), and the isotropic Navier–Stokes equation with a random stirring force of a very general form that covers, in particular, the overall shaking of the system and, in some limiting case, turbulent motion.

The obtained results reveal complex patterns of possible critical behaviour including: the lack of a fully nontrivial regime, for which nonlinear terms from both coupled equations would be simultaneously relevant in the sense of Wilson, non-universality, strong dependence on the type of random noise, non-conventional anisotropic scaling behaviour with a kind of dimensional transmutation, curves of simultaneously stable fixed points and so on.

Speaker: Polina Kakin

MQFT_Kakin.pdf

3:30 PM Renormalization group analysis of an anisotropic sandpile model: Effects of randomly moving isotropic environment

Employing the renormalization group method, we study the behavior of the explicitly anisotropic Hwa-Kardar sandpile model encompassed by an explicitly isotropic randomly moving medium. The motion of the medium is described by the stochastic Navier-Stokes equation with a random stirring force of a rather general form that includes, in particular, the overall shaking of the system and a non-local part with a power-law spectrum $k^{4-d-y}$ that describes, in the limiting case $y \to 4$, a turbulent pumping. The interplay between isotropic and anisotropic interactions results in a rich pattern of attractors of the RG flows in the space of the running coupling parameters, including fixed points, lines, and surfaces. The scaling dimensions corresponding to various asymptotic regimes are calculated perturbatively exactly (exactly to all orders of perturbation theory).

Moreover, the analysis of possible two-loop corrections suggests the existence of another nontrivial fixed point, not detectable within the one-loop approximation. If this point exists, it corresponds to a fully nontrivial regime where the Hwa-Kardar nonlinearity and advection by the turbulent fluid are simultaneously relevant. However, without practical two-loop calculations, the arguments supporting the existence of this fixed point are only preliminary and speculative. In particular, it is not clear whether the full-scale fixed point gives rise to a regular expansion in $y \sim \varepsilon$ or it cannot be treated within perturbation theory. This question remains for future study.

Speaker: Nikita Lebedev (N.N. Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research)

MQFT Lebedev.pdf

4:00 PM RG analysis of random walk on a KPZ fluctuating rough surface

The talk is devoted to the model of random walk on a fluctuating rough surface using the field-theoretic renormalization group (RG). The surface is modelled by the well-known Kardar-Parisi-Zhang (KPZ) stochastic equation while the random walk is described by the standard diffusion equation for a particle in a uniform gravitational field. In the RG approach, possible types of infrared (IR) asymptotic (long-time, large-distance) behaviour are determined by IR attractive fixed points. Within the one-loop RG calculation (the leading order in $\varepsilon=2-d$, $d$ being the spatial dimension), we found six possible fixed points or curves of points. Two of them can be IR attractive: the Gaussian point (free theory) and the nontrivial point where the KPZ surface is rough but its interaction with the random walk is irrelevant.

We also explored consequences of the presumed existence in the KPZ model of a non-perturbative strong-coupling fixed point. We found that it gives rise to an IR attractive fixed point in the full-scale model with the nontrivial spreading law $R(t)\sim t^{1/z}$, where the exponent $z$ can be inferred from the non-perturbative analysis of the KPZ model.

The talk is based on
N. V. Antonov, N. M. Gulitskiy, P. I. Kakin. A. S. Romanchuk "Random walk on a random surface: implications of non-perturbative concepts and dynamical emergence of Galilean symmetry" // J. Phys. A: Math. Theor. 58, 115001 (2025)

Speaker: Nikolay Gulitskiy (Saint Petersburg State University)

MQFT_Gulitskiy.pdf

2:30 PM → 4:30 PM Section D: Gravitation and cosmology

2:30 PM U(1) gauged nontopological solitons and boson stars in 3+1 dimensional O(3) sigma-model

We present and study new nontopological soliton solutions in the U(1) gauged nonlinear O(3) sigma-model with a symmetry breaking potential in 3+1 dimensional space-time. The configurations are endowed with an electric and magnetic field and also carry a nonvanishing angular momentum density. We discuss properties of these solitons and investigate the domains of their existence. The negative coupling constant of the scalar self-interactions allows for two types of boson stars: Type I solutions represent the usual boson stars, that emerge from the vacuum as the boson frequency is decreased below the boson mass, whereas type II boson stars emerge from a set of static soliton solutions. Depending on the strengths of the gravitational and the electric coupling constants, both types or only one type is present. At a critical set of coupling constants, both types undergo a bifurcation.

Speaker: Yakov Shnir (BLTP, JINR)

St-Petersburg-2025.pdf

3:00 PM Charged topological geons with a selfgravitating scalar field

A topological geon is an asymptotically (anti-)de Sitter or flat spacetime with topology $\mathbb{R}\times{}M$, where $M$ is the punctured projective space, $M=\mathbb{R}P^3\,\backslash\{p\}$, and the removed point $p$ corresponds to the spacelike infinity. The spacelike slice $M$ is conventionally obtained as the quotient $W/\mathbb{Z}_2$ of a symmetric wormhole $W$ by the isometric action of the binary group. We study the general properties of static, spherically symmetric, charge topological geons supported by a selfgravitating, minimally coupled scalar field with negative kinetic energy and an arbitrary potential. It turns out, in particular, that the total electric charge of a geon is completely determined by its mass and size, that is, the size of the corresponding wormhole throat. We find and discuss some exact solutions of the complete system of field equations.

Speaker: Alexander Tsirulev (Tver State University)

MQFT_Tsirulev.pdf

3:30 PM Quantum black holes at large D

We study a novel variation of the large D limit in which s-wave sector is described by a 2D gravity nearly decoupled from other modes, but temperature remains finite. We discuss the quantum description of such system and it's thermal behavior

Speaker: Oleg Novikov

Novikov_MQFT2025.pdf

4:00 PM On Thermodynamics of Evaporating Regular Black Holes

A black hole can evaporate through the mechanism proposed by Hawking. In the case of a Schwarzschild black hole, this leads to the temperature of the black hole increasing without bound as its mass decreases. However, if the black hole possesses multiple horizons, as in the case of regular black holes, the picture changes dramatically. In our work, we analyze the behavior of the Hawking temperature for evaporating regular black holes and demonstrate that, in the presence of an inner horizon, the temperature either decreases monotonically to zero or increases slightly before monotonically decreasing to zero during the evaporation process.

Speaker: Vitalii Vertogradov (Herzen State Pedagogical University of Russia)

Vertogradov.pdf

4:30 PM → 5:00 PM Coffee

5:00 PM → 6:40 PM Section A: Mathematical methods in QFT

5:00 PM Casimir energy of a scalar field rotating on a disk

We compute the vacuum energy of a scalar field rotating with angular velocity Ω on a disk of radius R and with Dirichlet boundary conditions. The rotation is introduced by a metric obtained by a transformation from a rest frame to rotating frame. To compute the vacuum energy, we use an imaginary frequency representation and the well-known uniform asymptotic expansion of the Bessel function. We use the zeta-functional regularization and separate the divergent contributions, which we discuss in terms of the heat kernel coefficients. The divergences are found to be independent of rotation. The renormalized finite part of the vacuum energy is negative and becomes more negative for larger rotation frequencies.

Speaker: Irina Pirozhenko (BLTP JINR)

talk_MQFT2025.pdf

5:20 PM First-order GLSM construction in sigma models

Sigma models constitute a fundamental class of field theories with wide-ranging applications in theoretical and mathematical physics. However, their analysis is often complicated by the nonlinearity of their Lagrangians. While traditional approaches, such as the background field method, offer partial insights, they face inherent limitations.

In this talk, I will present an alternative framework—the first-order GLSM formulation (or Gross-Neveu formalism)—which reformulates sigma models as gauge theories with a finite number of interactions via symplectic reduction. This approach provides a powerful tool for studying sigma models with homogeneous Hermitian target spaces associated with classical Lie groups. I will discuss the key aspects of this method, its advantages over conventional techniques, and its implications for nonperturbative analysis.

The results are based on joint work with Dmitri Bykov:
arXiv:2306.04555
arXiv:2407.20423
arXiv:2502.07612

Speaker: Viacheslav Krivorol (Institute for Theoretical and Mathematical Physics (MSU) and Steklov Mathematical Institute, Moscow)

Gross_Neveu_for_MQFT.pdf

5:40 PM Explicit Construction of states in the orbifolds of N=2 Minimal models of ADE type

We propose the explicit construction of fields in the orbifolds of products of $N=(2,2)$ minimal models with ADE invariants. It is shown that spectral flow twisting by the elements of admissible group $G_{\text{adm}}$, is consistent with the nondiagonal pairing of D and E type minimal models. We obtain the complete set of fields of the orbifold from the mutual locality and other requirements of the conformal bootstrap. The collection of mutually local primary fields is labeled by the elements of mirror group $G^{*}_{\text{adm}}$. The permutation of $G_{\text{adm}}$ and $G^*_{\text{adm}}$ is given by the mirror spectral flow construction of the fields and transforms the original orbifold into a mirror one.
This transformation is by construction an isomorphism of $N=(2,2)$ models.
We illustrate our construction for the orbifolds of $\textbf{A}_{2}\textbf{E}_7^{3}$ model.}

Speaker: Boris Eremin (Institute for Information Transmission Problems RAS, Skoltech)

Explicit_construction_of_states_in_orbifolds_of_products_of_N_2_Superconformal_ADE_Minimal_models.pdf

6:00 PM On the relevance of quantum corrections to the matter stress-energy tensor in eternally expanding universes

We study a toy-model of continuous infinite expansion of space-time with the flat start. We use as the gravitational background a conformaly flat metric with growing factor in conformal time. We aim to clarify some properties of quantum fields in such a gravitational background. In particular, we calculate one-loop corrections to the Keldysh propagator to verify the fact of secular growth of the occupation number and anomalous quantum average in the massless scalar field theory with selfinteractions and separately in the massive scalar field theory with $\xi=1/6$. We perform the calculation in arbitrary dimensions with the use of the Schwinger-Keldysh technique. We get a secular growth which is not of a kinetic type. We provide some results for the case of generic interaction $\frac{\lambda}{b!}\phi^b$.

Speaker: Kirill Kazarnovskii (MIPT)

Kazarnovskii_slides_mqft25.pdf

6:20 PM Multipoint conformal integrals

We present a new framework for evaluating multipoint one-loop parametric conformal integrals in arbitrary dimensions. Our approach, called reconstruction, is based on a diagrammatic algorithm which systematically builds a class of multivariate generalized hypergeometric series in terms of a convex polygon which is part of the Baxter lattice. The talk is based on joint work with K.B. Alkalaev.

Speaker: Semyon Mandrygin (Lebedev Physical Institute)

MQFT_2025_Mandrygin.pdf

5:00 PM → 6:40 PM Section C: Field theoretical methods in statistical physics

5:00 PM Investigation of asymptotic behaviours in the $O(n)$-symmetric $\varphi^4+\varphi^6$ theory based on six-loop calculations

Tricritical behavior in systems with an $n$-component order parameter $\varphi = \{\varphi_k, k = 1, \ldots, n\}$ is described by the action
\begin{equation}
S(\varphi) = \frac{1}{2}\partial_i\varphi_k\partial_i\varphi_k + \frac{\tau_0}{2} \varphi_k\varphi_k + \frac{\lambda_0}{4!} (\varphi_k\varphi_k)^2 + \frac{g_0}{6!} (\varphi_k\varphi_k)^3,
\end{equation}
where the coefficients $\tau_0$, $\lambda_0$ and $g_0$ are parameters of the model [1].

Tricritical asymptotics correspond to the situation where $\tau_0 \sim \lambda_0 \rightarrow 0$. Depending on the relative smallness of the parameters $\tau_0$ and $\lambda_0$, the analysis at the canonical dimension level predicts three possible asymptotic behaviors:

1. Tricritical -- the $\varphi^4$ interaction is not significant;
2. Modified Critical -- the $\varphi^6$ interaction is not significant;
3. Combined Tricritical -- both interactions are significant.

It is possible to enter a parameter $\alpha$, which depends on the trajectory of the approach to the tricritical point in the experiment, and at different values of which, different asymptotic behaviours will be observed. At a certain value $\alpha = \alpha_0$, the combined tricritical behavior will occur; when $\alpha > \alpha_0$, tricritical behavior is observed, and when $\alpha < \alpha_0$, modified critical behavior occurs.

Renormalization group analysis which was fully conducted by Vasil'ev [1] allows us to refine the value of the parameter $\alpha_0$. Additionally, the renormalization group analysis shows that for $\alpha = \alpha_0$, not only the combined tricritical behavior is possible, but also modified critical behavior. It depends on the parameter $a$ that occurs during the analysis. If $a$ turns out to be positive, there are two possible behaviours and the parameter determines the boundary value for the relative amplitude of $\tau_0$ and $\lambda_0$, at which the transition between different behaviours occurs. Otherwise, only the combined tricritical behaviour is possible. In the main order, the parameter $a$ was calculated by Vasil'ev [1] and it is positive. Therefore, the first situation is realized to the lowest approximation. We are investigating the effect of six-loop corrections on the parameter $a$.

The work is supported by the Ministry of Science and Higher Education of the Russian Federation (agreement no. 075–15–2022–287).

[1] A.N. Vasil’ev, Quantum field renormalization group in critical behavior theory and stochastic dynamics. Chapman and Hall/CRC (2004).

Speaker: Aleksandr Trenogin (SPbU)

mqft_2025_Trenogin.pdf

5:20 PM Diagram reduction in the models of critical dynamics

In this talk, using the calculation of the dynamic critical exponent $z$ in the Model A in the four-loop approximation as an example, we will present the diagram reduction technique. This method allows for a substantial decrease in both the number of diagrams and divergent dynamic subgraphs, thereby facilitating subsequent parametric integration with Goncharov polylogarithms.

Speaker: Diana Davletbaeva (SPbU, NRC «Kurchatov Institute» - PNPI)

mqft2025_Davletbaeva.pdf

5:40 PM Parametric integration in the models of critical dynamics

This talk presents the application of parametric integration with Goncharov polylogarithms to multiloop analytic calculations in models of critical dynamics. The technique has been successfully applied in various high-energy physics and static critical models. Its main requirement is linear reducibility of the integrals under evaluation. In dynamical models, linearly non-reducible integrals already appear at low-loop orders and their analytic structure differs from that in static models.

We discuss the application of the parametric integration in the model of stochastic turbulence in the $d\to\infty$ limit and the model A based on $\phi^4$-theory, both in the four-loop approximation. Also, the model A based on $\phi^3$-theory is considered, where the two-loop order is obtained analytically. We propose a method to evaluate linearly non-reducible dynamical integrals based on splitting the integrand into separately reducible streams. The approach can be applied to diagrams in any model, where standard techniques, such as changes of variables, fail to restore reducibility.

Speaker: Daniil Evdokimov (SPbU, JINR)

Vasil_ev_conference_talk_Evdokimov.pdf

6:00 PM Random Walks in a Dynamic Environment

The renormalization-group approach is used to investigate the possible IR behavior of a randomly walking particle in a random dynamic environment. The particle movement is modeled by the stochastic Fokker -- Planck equation. The dynamics of the environment are described by a random drift field $F_j$ with a pair correlator, which implies two limiting cases -- a "rapidly-changing" and time-independent ("frozen") drift field respectively. The stochastic problem is reformulated in terms of quantum field theory with a given action functional. The ultraviolet divergences are eliminated multiplicatively. The renormalization group equation has five attractors in the form of two-dimensional fixed points in the parameter space. Three of them are associated with the super-diffusion and sub-diffusion scaling regimes, when the normal propagation law for a particle cloud $R(t)\simeq t$ is violated.

Speaker: Andrew Babakin (Department of Physics, Saint Petersburg State University, Universitetskaya nab. 7/9, 199034 St. Petersburg, Russia; st068365@student.spbu.ru)

MQFT2025_Babakin.pdf

6:20 PM Random walk on a rough surface: Conservation law and renormalization group

The field-theoretic renormalization group (RG) method was used to study the behavior of a randomly walking particle on a rough surface. The surface was given by the conserved Kardar--Parisi--Zhang (CKPZ) stochastic equation, and the random walk was governed by the standard diffusion equation for a particle in a uniform gravitational field. The complete model was presented as a field-theoretic model, which was found to be multiplicatively renormalizable and logarithmic for $ d = 2 $. The RG equation allowed us to identify stable fixed points corresponding to possible types of infrared (IR) asymptotic (long-time, large-distance) behavior. All critical dimensions were found exactly. In particular, the spreading law for the particle’s cloud was established, which differs from the standard expression $ R^2(t) \sim t $.

Speaker: Aleksandr Luchin (Saint Petersburg State University)

MQFT2025_Luchin.pdf

5:00 PM → 6:40 PM Section D: Gravitation and cosmology

5:00 PM Accretion in the early Universe and charge asymmetry

Coexistence of heavy particles and primordial black holes in early Universe can result in baryon asymmetry production. It requires C and CP symmetries violation of particles scattering on relativistic symmetric plasma. Generation mechanism is considered with including expansion effects. Several possible realizations can be considered with different resulting asymmetry and available parameters space.

Speaker: Nikolay Pozdnyakov (Novosibirsk State University)

Pozdnyakov.pdf

5:20 PM False vacuum decay around black holes

We perform numerical semiclassical calculations of the false vacuum decay probability for a scalar field in the Schwarzschild spacetime. The suppression $F$ of the decay probability $P \sim e^{-F}$ is given as a functional of a semiclassical solution. That solution is defined on a certain contour in complex time. We consider a model with potential $V(\phi) = \frac{1}{2}m^2 \phi^2 - \frac{1}{2} m \sqrt{\lambda} \phi^3$. Semiclassical solutions were obtained numerically and used to calculate the decay probability around black holes of different masses. It was found that the decay probability remains exponentially suppressed in the limit of small black hole mass.

Speaker: Ratmir Gazizov (MSU & INR RAS)

MQFT_2025.pdf

5:40 PM Barotropic Equation of State and Nonlinear Electrodynamics in Dynamical Black Hole Spacetimes

Models of black holes that differ from idealized vacuum and electrovacuum solutions of Einstein's equations often contain parameters whose physical interpretation is unclear. However, to propose a black hole model for experimental verification, we must clearly understand which parameters describe the black hole and what physical constraints can be imposed on each parameter. When considering dynamical black holes with a barotropic equation of state, an additional integration constant arises, the nature of which remains unclear except for a few specific values of the equation of state coefficient. Nevertheless, when examining solutions such as Husain or Kiselev, we can observe remarkable effects related to black hole evaporation, which are associated with the violation of null energy conditions. However, the main issue lies in the fact that while violations of energy conditions may occur in nature, the ambiguity in the values of parameters describing black holes makes it difficult to determine whether such violations result from natural physical processes or are purely mathematical artifacts that should be excluded from consideration. Moreover, energy conditions play a crucial role in the evolution of a black hole shadow - a characteristic that can potentially be observed experimentally. In this article, we elucidate the parameter arising in Husain's and Kiselev's solutions using nonlinear electrodynamics. We demonstrate that for physically relevant equations of state, the additional parameter represents a combination of electric and magnetic charges.

Speaker: Dmitriy Kudryavcev (Herzen State Pedagogical University of Russia)

Kudryavcev.pdf

6:00 PM Blinking islands in charged black holes

In this talk, we will explore the dynamics of entanglement entropy and entanglement islands within a two-sided Reissner-Nordström black hole placed in a cavity bounded by a reflecting wall. This setup alters the dynamics of entanglement entropy, causing it to saturate at a value that is potentially lower than the thermodynamic entropy of the black hole, which contradicts the Page curve paradigm. A key finding is the temporary disappearance of the entanglement island, known as the "blinking island" effect, which periodically re-establishes the information paradox. We will discuss and compare these entanglement behaviors with the thermodynamic stability of the black hole.

Speaker: Anastasia Zueva (Steklov Mathematical Institute)

Zueva.pdf

6:20 PM Axion-mediated electron-electron interaction in RaOCH$_3$ molecule for Dark matter searches

Pseudoscalar particles called axions are promising candidates for dark matter constituents [1]. The hypothetical interaction of axions with leptons (e.g., electrons) produces an effective electron-electron interaction. When considering electrons in hexatomic molecules, e.g., RaOCH$_3$, such interaction via axion exchange is capable of violating the parity parity of molecular Hamiltonian. Thus, the theoretical description and experimental study of the electronic structure of such molecules is an excellent way to investigate the $\mathcal{P}$, $\mathcal{T}$-violation effects.

The theoretical description of such systems requires taking into account vibrations and rotations. In order to do so, one should perform calculations with different configurations of the molecule to account for changes in the studied properties. To reduce computational costs, we use the generalized effective core potential (GRECP) to describe the core electrons [2].

The molecular spinors obtained using GRECP have incorrect smoothed behavior in the core region, and parity violation effects are enhanced precisely near the nucleus. To overcome that problem, the one-center restoration (OCR) technique [3] is applied. The latter method has previously been used [4] to calculate one-electron properties; in the current work we generalize it to the case of two-electron properties and apply it to obtain the enhancement parameter for the axion-mediated electron-electron interaction.

The work was supported by the Russian Science Foundation Grant No. 24-72-10060 (https://rscf.ru/project/24-72-10060/).

[1] Preskill, John, Mark B. Wise, and Frank Wilczek. "Cosmology of the invisible axion." {\it{Physics Letters B}} 120.1-3 (1983): 127-132.
[2] Titov, A. V., and N. S. Mosyagin. "Generalized relativistic effective core potential: Theoretical grounds." {\it{International journal of quantum chemistry}} 71.5 (1999): 359-401.
[3] Titov, A. V., et al. "P, T-parity violation effects in polar heavy-atom molecules." {\it{Recent Advances in the Theory of Chemical and Physical Systems}} 253 (2006): 253-283.
[4] Zakharova, Anna. "Symmetric top molecule YbOCH3 in the fundamental P, T-violation searches." {\it{Chemical Physics Letters}} 854 (2024): 141552.

Speaker: Mikhail Reiter (Saint-Petersburg State University)

Reiter.pdf

Wed, October 8

10:00 AM → 11:20 AM Plenary Session

10:00 AM AdS Harmonic Superspace from N=2 Superconformal Group

Harmonic ${\cal N}=2$ superspace was discovered in 1984 as the powerful unique tool of the geometric superfield off-shell description of ${\cal N}=2, 4D$ supersymmetric field theories with the maximal spins 1, 2, and 1/2 (${\cal N}=2$ Yang-Mills theories, supergravity and matter hypermultiplets). Later on, harmonic superspace methods were successfully applied to set up the previously unknown off-shell formulations of the gauge ${\cal N}=2$ higher-spin theories in terms of the unconstrained analytic ${\cal N}=2$ superfields, in both conformal and non-conformal cases. Based on a recent work with Nikita Zaigraev, I show how to deduce ${\cal N}=2$ higher-spin theories on AdS$_4$ superbackground, proceeding from the harmonic superspace realizations of ${\cal N}=2$ superconformal symmetry $SU(2,2|2)$.The basic idea is to introduce a constant isotriplet $c^{ik}$ that breaks $SU(2,2|2)$ down to AdS$_4$ supersymmetry $OSp(2|4;R)$. The superfield Weyl transformation relating ordinary ${\cal N}=2$ harmonic superspace to its AdS$_4$ deformation is defined and $OSp(2|4;R)$-invariant action of massive hypermultiplet is derived, employing this transform.

Speaker: Evgeny Ivanov (BLTP JINR)

EIvanovSPb25.pdf

10:40 AM Conformal four-point ladder integrals in diverse dimensions and classical polylogarithms

In our previous works, we used the graph-building operator technique, together with the connection to conformal quantum mechanics, to obtain an all-loop result for the conformal ladde and zig-zag four-point diagrams in arbitrary dimensions. While our expression for ladder diagrams was fully analytical and valid in any dimension, it was formulated in terms of Gegenbauer polynomials, so despite its generality the form of the answer could be subtle for the practical use. In the present report, we show that in arbitrary even dimensions our previous representation can be systematically expressed using classical polylogarithms and rational functions. We also verify that our representation satisfies dimensional shift (D -> D+2) identity.

Speaker: Alexey Isaev (BLTP, JINR)

Isaev-Piter-2025.pdf

11:20 AM → 11:40 AM Coffee

11:40 AM → 1:40 PM Plenary Session

11:40 AM Flowing with Gravity: The Holographic Renormalization Group

The holographic duality provides a powerful framework for understanding strongly interacting conformal field theories, and more generally, quantum field theories. The AdS/CFT correspondence, its prime and most concrete example, is largely based on the connection between the isometry group of the AdS spacetime and the conformal group, but is not exhausted by this.
The main statement of the holographic duality says that a gravitational theory in a d-dimensional spacetime is completely equivalent to a non-gravitational quantum theory living on its (d-1)-dimensional boundary. Thus, we are able to extract information on QFT observables at strong coupling by performing calculations on the gravitational side of the duality.
However, neither the bulk gravity theory nor the dual field theory is free from pathological divergent behavior. To find correct relations for quantities, it is necessary to perform the holographic regularization and renormalization to remove divergences systematically and consistently. These procedures are similar to those in QFT. As in QFT, the renormalization procedure in holography leads to the notion of renormalization group flows proposed in the works of E. Akhmedov, K. Skenderis, J. de Boer, E. and G. Verlinde. From the holographic side, RG flows are described in terms of gravitational domain walls with AdS boundaries and certain boundary conditions for the bulk fields. In particular, thanks to the boundary conditions, the gravitational Hamiltonian equations can be reduced to the form of the Callan-Symanzik equation. The holographic RG flow is associated with the RG flow of the dual field theory between conformal fixed points, triggered either by a relevant operator or a non-zero VEV of an operator. The UV divergences of the dual field theory correspond to the IR divergences on the gravitational side.
A special case is represented by thermal RG flows, which allow us to study the consistency of dual CFTs and the dynamics of the near-horizon region of black holes. In the framework of holographic duality, the RG flows at finite temperature are described by asymptotic AdS black holes, and their behavior near the horizon encodes the thermalization process in the dual CFT.
In my talk I give a review of basic aspects and recent progress of holographic RG flows at zero and finite temperatures and present a way of studying them through the dynamical systems.

Speaker: Anastasia Golubtsova (BLTP JINR)

MQFT25golubtsova.pdf

12:20 PM Sigma models from Gaudin spin chains

We solve the classical and quantum problems for the 1D sigma model with target space the flag manifold U(3)/U(1)^3, equipped with the most general invariant metric. In particular, we explicitly describe all geodesics in terms of elliptic functions and demonstrate that the spectrum of the Laplace-Beltrami operator may be found by solving polynomial (Bethe) equations. The main technical tool that we use is a mapping between the sigma model and a Gaudin model, which is also shown to hold in the U(n) case.

This talk is based on a series of joint papers with A. Kuzovchikov and V. Krivorol:

• D. Bykov and A. Kuzovchikov. “The classical and quantum particle on a flag manifold”. arXiv:2404.15900 [hep-th]
• D. Bykov, V. Krivorol and A. Kuzovchikov. “Oscillator Calculus on Coadjoint Orbits and Index Theorems”. arXiv:2412.21024 [hep-th]
• D. Bykov and A. Kuzovchikov. “Sigma models from Gaudin spin chains”. arXiv:2508.20889 [hep-th]

Speaker: Dmitri Bykov (S)

Talk MQFT St. Petersburg 2025 2.pdf

Talk MQFT St. Petersburg 2025.pdf

1:00 PM Green functions of field theory with the use of stochastic integral

Functional representations for the generating function of field-theoretic Green functions of the stochastic differential equation with multiplicative noise are constructed with the use of the stochastic integral of Itô. Differences in the functional representations due to interpretations of Itô and Stratonovich of the stochastic differential equation are pointed out.

Speaker: Juha Honkonen (Department of Physics, University of Helsinki)

MQFT2025 Honkonen.pdf

1:40 PM → 3:00 PM Lunch

3:00 PM → 7:00 PM Excursion

Thu, October 9

10:00 AM → 11:20 AM Plenary Session

10:00 AM A way to constrain a graviton mass from astronomical observations

The first version of the massive theory of gravity was introduced by Fierz and Pauli in 1939. In 1972 Boulware and Deser found ghosts in massive theories of gravity and physicists concluded that such theories hardly ever could be realizable in nature. Several years ago C. de Rham and her co-authors showed that there is an opportunity to create massive theories of gravity without ghosts (see, [1] for reference). In the first LIGO-- Virgo paper where the authors reported about the discovery of gravitational waves and discovery of binary black hole systems it was also reported about graviton mass constraint. Soon after that we showed that similar constraints could be obtained from observations of bright stars near the Galactic Center done by VLT -- GRAVITY collaboration and Keck group observing the Galactic Center (leaders of these groups R. Genzel and A. Ghez were awarded by Nobel prize in 2020). Our constraint on graviton mass was included in PDG https://pdg.lbl.gov/2025/listings/rpp2025-list-graviton.pdf and in the fundamental book on the subject [1]. One can find references at our 8 papers on the subject in a recent GRAVITY paper [2].
We discuss other ways to constrain graviton mass from other astronomical observations.

[1]. C. de Rham, A. Tolley, The Encyclopedia of Cosmology, Set 2: Frontiers in Cosmology, Volume 1. Modified Gravity, Editor-in-chief: Giovanni G Fazio, World Scientific, Singapore (2024).

[2]. [9]. GRAVITY Collaboration, Astron. Astrophys. 698, L15 (2025) https://www.aanda.org/articles/aa/full_html/2025/06/aa54676-25/aa54676-25.html

Speaker: Alexander Zakharov (ITEP, BLTP JINR)

Zakharov_Vasiliev_09_10_2025.pdf

Zakharov_Vasiliev_09_10_2025.ppt

10:40 AM Possible types of dark matter condensation in embedding gravity

We investigate the possibility of explaining the observed effects usually attributed to the existence of dark matter through a transition from GR to a modified theory of gravity - embedding gravity. Since this theory can be reformulated as GR with additional fictitious matter of embedding gravity (FMEG), which moves independently of ordinary matter, we analyse solutions in which FMEG behaves similarly to cold dark matter. An upper bound on the possible density of FMEG is obtained, which explains the absence of dark matter effects on small scales. Possible static condensed structures of FMEG are found, which can be reduced to configurations of the types wall, string, and sphere. In the latter case, FMEG exhibits the properties of an isothermal ideal gas which has a linear equation of state. The emerging spherical condensations of FMEG create potential wells that facilitate galaxy formation. For large values of the radius, the corresponding density distribution profile behaves in the same way as the pseudo-isothermal profile (ISO), which is successfully employed in fitting galactic dark halo regions, and provides flat galactic rotation curves.

Speaker: Sergey Paston (Saint Petersburg State University)

paston-mqft25.pdf

11:20 AM → 11:40 AM Coffee

11:40 AM → 1:00 PM Plenary Session

11:40 AM Geodesics and Global Properties of the Liouville Solution in General Relativity with a Scalar Field

One parameter family of exact solutions in General Relativity with a scalar field has been found using the Liouville metric. The scalar field potential has exponential form. The solution corresponding to the naked singularity provides smooth extension of the Friedmann Universe with accelerated expansion through the zero of the scale factor back in time. All geodesics are found explicitly. Their analysis shows that the Liouville solution is a global one: every geodesic is either continued to infinite value of the canonical parameter in both directions or ends up at the singularity at its finite value. Moreover, analysis of geodesics shows that the naked singularity located outside the
Friedmann Universe attracts matter and therefore provides its accelerating expansion inside the light cone.
[1] D. E. Afanasev, M. O. Katanaev, “Liouville solution in General Relativity with a scalar field”, Phys. Lett. B, 864 (2025), 139439 , 5 pp.
[2] D. E. Afanasev, M. O. Katanaev, “Geodesics and global properties of the Liouville solution in general relativity with a scalar field”, JCAP, 2025:08 (2025), 045, 29 pp.

Speaker: Mikhail Katanaev (Steklov Mathematical Institute)

Katanaev_Cosmological_model.pdf

12:20 PM Compensation of vacuum energy by scalar field coupled to curvature

We propose a dynamical mechanism of vacuum energy cancellation by a scalar field $\phi$ coupled to curvature scalar as $\beta R \phi^2 f(\phi)$ where $f(\phi)$ is a polynomial function of $\phi$. It is shown that the exponential expansion driven by vacuum energy is dynamically transformed into the standard cosmological evolution of a radiation-dominated universe.

Speaker: Elena Arbuzova (Dubna State University and Novosibirsk State University)

Piter-MQFT2025-ArbuzovaE.pdf

1:00 PM → 2:30 PM Lunch

2:30 PM → 4:30 PM Section B: Quantum field theory methods in elementary particle physics

2:30 PM A simple generalization of the low-energy theorem for the effective Higgs-gluon-gluon coupling for the case of simultaneous decoupling of several heavy quarks

We extend in a simple way the well-known low-energy theorem for an effective Higgs-like scalar-gluon-gluon coupling in QCD including arbitrary number of heavy quarks in addition to the light ones. The application of the extended low-energy theorem leads to a new result: an extraction of the four-loop effective Higgs-gluon-gluon coupling valid for extensions of the Standard Model with additional heavy quarks from the 3-loop results of A.G. Grozin et al (2011) for the decoupling constant of $\alpha_s$.

Speaker: Konstantin Chetyrkin (ИЯИ РАН)

dec25_Leningrad_251009_120601.pdf

3:00 PM New aspects of gauge-gravity relation

New aspects of gauge-gravity relation

The relation between four-dimensional $SO(4)$ pure Yang-Mills theory
and the gravity is discussed. The functional integral for Yang-Mills theory is rewritten in terms of the gravity metric and Riemann tensors.
Its peculiar feature is the cosmological term added to the Einstein-Hilbert action. This relation is shown to also provide a simple way to derive the linear potential resulting from the average Wilson loop in
$SO(4)$ pure Yang-Mills theory.

Published in
Phys. Rev. D 111, no.6, 066023 (2025)

Speaker: Andrei Shuvaev (NRC "Kurchatov Institute" - PNPI, Gatchina 188300 Russia)

Shuvaev.pdf

3:30 PM Production of relativistic composite particles via the mechanism of coherent coalescence

We study the formation of composite weekly bound particles with large transverse momentum by means of the coalescence mechanism in high-energy hadron collisions. We find the coalescence coefficient by calculating the corresponding Feynman diagrams near the kinematic boundary, taking into account the coherent nature of the process. In this approximation, we calculate the dependence of the coalescence coefficient on the emission angle and energy. We also present a physical interpretation of the obtained results.
At the nucleon level, the developed approach can be applied to describe the formation of light nuclear fragments with high transverse momentum, for example, the production of deuterons in dd collisions, which is relevant for the physics research program of SPD at NICA. At the quark level, this approach can be used to calculate Feynman diagrams describing the production of baryons with large transverse momenta near the kinematic boundary in high-energy pp and AA collisions due to the process of coherent coalescence of quarks, which is also relevant for the SPD and MPD experiments planned at the NICA collider.

The authors are grateful to Saint-Petersburg State University for research project 103821868.

Speaker: Vladimir Vechernin (St. Petersburg State University)

Vechernin-MQFT-2025.pdf

4:00 PM The Regge-Gribov model with pomerons and odderons

The Regge-Gribov model describing interacting pomerons and odderons is proposed with triple reggeon vertices taking into account the negative signature of the odderon. Its simplified version with zero transverse dimensions is first considered. No phase transition occurs in this case at the intercept crossing unity. This simplified mosel is studied without more approximations by numerical techniques.

The physically relevant model in the two-dimensional transverse space is then studied by the renormalization group method in the single loop approximation. The pomeron and odderon are taken to have different bare intercepts and slopes. The behavior when the intercepts move from below to their critical values compatible with the Froissart limitation is studied. Five real fixed points of the renormalization group flow are found with singuarities of the propagators in the form of non-trivial branch points indicating a phase transition as the intercepts cross unity. The new phases, however, are not physical, since they violate the projectile-target symmetry. In the vicinity of fixed points the asymptotical behavior of Green functions and elastic scattering amplitude is found under Glauber approximation for couplings to participants.

Speaker: Mikhail Vyazovsky (Saint-Petersburg State University)

Vyazovsky.pdf

2:30 PM → 4:30 PM Section D: Gravitation and cosmology

2:30 PM Deviation of trajectories in General relativity and non-relativistic mechanics and Shirokov effect

Features of deviation of circular trajectories in the central field in non-relativistic and relativistic cases are investigated. All potentials for which perturbed trajectories in the non-relativistic case are closed and asymptotically flat spherically symmetric metrics with closed perturbed orbits are found. It is shown that in the general theory of relativity there are metrics in which the frequencies of oscillations of perturbed orbits in all directions coincide, i.e. the Shirokov effect is absent. General formulas are obtained for the shift of the pericenter of perturbed orbits in the non-relativistic case and in the general theory of relativity. An estimate of the influence of the cosmological constant on the deviation of trajectories and on the Shirokov effect during rotation in the Schwarzschild gravitational field has been obtained.

Speaker: Yuri Pavlov (Institute for Problems in Mechanical Engineering of the Russian Academy of Sciences, Saint Petersburg)

Pavlov_MQFT_25.pdf

3:00 PM IR-effective quantum gravity in a theory with a cosmological constant: a renormalization group study of the gravitational potential at large distances.

The standard non-renormalizable action of quantum gravity without the contribution of matter
\begin{equation}
S = \frac{1}{2\kappa} \int d^4x \sqrt{-g} \left( R - 2\Lambda \right).
\end{equation}

is investigated.

Dimensional analysis, generally accepted in the study of continuous phase transitions in statistical physics, has obtained and the infrared-effective action for describing the theory at large distances was obtained. This action is renormalizable, the logarithmic dimension is $d=5+1$.

The quantum field renormalization group method is used to construct a $5+1-\epsilon$ expansion of the Green's functions of gravitons. In the one-loop approximation, a power-law behavior of the gravitational potential at large distances (the power differs from $1/r$ ) and an increase in effective masses are detected. All this is the result of taking into account the self-ineraction of massless gravitons in the IR region.

Speaker: Mikhail Nalimov (SPdU)

nalimov_en.pdf

3:30 PM Isometric embedding of the gravitational pp-wave

Isometric embedding of a pseudo-Riemannian spacetime is a description of this spacetime as a surface in an ambient spacetime of higher dimension. This procedure has been used for more than a century in the examination of solutions of Einstein equations, since the embedding class (i.e. the minimal codimension of a surface in a flat ambient spacetime) is an invariant characteristic of a spacetime.

Isometric embeddings are also used in modifying gravity within the so-called Regge-Teitelboim approach [1].

Embedding procedure for a spacetime with a given metric reduces to satisfying a condition of the metric inducibility:
\begin{equation}
\partial_\mu Y^a \partial_\nu Y^b \eta_{ab} = g_{\mu\nu}(x)
\end{equation}
where $Y$ is the embedding function, and $\eta$ and $g$ are the metrics of the ambient and embedded spaces, respectively.

In 2012, S. A. Paston proposed [2] a group-theoretic method for the separation of variables in this system. Using this method, all possible global minimal symmetric embeddings were found for the Friedmann model, non-rotating black holes (Schwarzschild-(anti) de Sitter and Reissner-Nordström-(anti) de Sitter), the BTZ black hole, and others.

Embeddings of gravitational wave metrics have been studied very poorly. Apart from mentions of a few specific cases of embeddings in the literature, a systematic investigation of this embedding, to our knowledge, has only been attempted once in [3]. However, the author of that work, employing the method of solving the Gauss-Codazzi equations, apparently did not aim to find the explicit form of the embeddings, and therefore only a few particular examples of the obtained surfaces are provided. Furthermore, some possible types of surfaces remained unstudied.

This work is devoted to a systematic study of embedded surfaces with the metric of gravitational pp-wave:
\begin{equation}
ds^2 = 2H(u,y,z)du^2-2dudv-dy^2-dz^2,
\end{equation}
where H is an arbitrary function whose transverse Laplacian is zero, and u and v are light-cone coordinates. The ambient space is chosen to be 2+4-dimensional because, according to [4] and [5], such an embedding can not exist in a 5-dimensional or globally hyperbolic space. We construct the surfaces using two ansatzes for the embedding function: the one used in [3] and the one given by method described in [2].

The obtained embeddings can be used for the analysis of gravitational wave solutions in the Regge-Teitelboim equations.

References

1. Sheykin A. A., Paston S. A. The approach to gravity as a theory of embedded surface // AIP Conference Proceedings. 2014. V. 1606. P. 400.
2. Paston S. A., Sheykin A. A. Embeddings for Schwarzschild metric: classification and new results // Class. Quant. Grav. 2012. V. 29. P.095022.
3. Collinson, C. D. Embeddings of the Plane-Fronted Waves and Other Space-Times // J. Math. Phys. 1968. V. 9. P. 403.
4. Kasner, E. Geometrical Theorems on Einstein's Cosmological Equations // Am.J.Math. 1921. V.43. N.4. P.217.
5. Penrose, R. A Remarkable Property of Plane Waves in General Relativity // Rev. Mod. Phys. 1965. V. 37. P. 215.

Speaker: Anton Sheykin (Saint Petersburg State University)

MQFT2025.pdf

4:00 PM Horndeski theory after Kaluza-Klein compactification

The application of the Horndeski theory in late-time cosmology is strongly limited by the strict coincidence of the propagation speeds of gravitational and electromagnetic waves. This restriction assumes that a photon with minimal coupling is not modified even at scales at which General Relativity (GR) may need modification. We have shown that the four-dimensional Galileon, obtained as a result of the Kaluza-Klein compactification of its five-dimensional version, can be considered as a natural modification of GR and electromagnetism. In this theory, gravitational waves propagate at the speed of light, which means that there is no need for fine-tuning the Galileon potential. This allows for a wider range of theories than was previously considered.

Speaker: Sergey Mironov (INR RAS & ITMP & ITEP)

MQFT_2025_mironov.pdf

2:30 PM → 4:30 PM Section E: Integrable models, symmetries in QFT and quantum groups

2:30 PM Constant solutions to Reflection Equation over basic quantum supergroups

We list K-matrices for the general linear and orthosymplectic quantum supergroups with the simplest "symmetric" triangular decomposition. This classification is based on a theory of super-spherical coideal subalgebas in quantum supergroups associated with Z_2-graded Satake diagrams. This theory extends quantum symmetric pairs of Letzter-Kolb to the realm of quantum supergroups.

Speaker: Andrey Mudrov (MIPT)

MQFT_Mudrov.pdf

3:00 PM Coproducts for affine super Yangians

For affine special superalgebra $\mathfrak{\hat{g}}(\Pi)$ defined by an arbitrary systems of simple roots $\Pi$ we define the affine super Yangian $Y_{\hbar}(\hat{g}(\Pi))$ as Hopf superalgebra which is a quantization of superbialgebra $\hat{g}(\Pi)[t]$ and describe super Yangian in terms of minimalistic system of generators. We consider Drinfeld presentation for $Y^D_{\hbar}(\hat{g}(\Pi))$ and prove that these two presentations are isomorphic as associative superalgebras. We induce by means of this isomorphism a comultiplication on Drinfeld presentation $Y^D_{\hbar}(\hat{g}(\Pi))$ of the super Yangian. We introduce action of Weyl groupoid by isomorphisms on super Yangians as extension of its action on universal enveloping algebra and deformation of action on universal enveloping superalgebra of current Lie superalgebra and prove that such extension is exist and unique. We also discuss the possibility of generalizing the considered constructions to the case of the Yangian of affinization $\hat{\mathfrak{g}}$ of the basic Lie superalgebra $\mathfrak{g}$.

Speaker: Vladimir Stukopin (Moscow Institute of Physics and Technology)

Stukopin_MQFT_2025.pdf

3:30 PM Improved non-Abelian tensor multiplet action

In this talk, construction of the superfield action of the $N = (1, 0)$, $d = 6$ non-Abelian tensor multiplet based on the non-Abelian tensor hierarchies is discussed. The supersymmetric systems of tensors with non-Abelian gauge symmetries are considered to be necessary tools for low-energy effective description of multiple M5-branes, as well as superconformal theories in six dimensions. The proper actions of such systems are not known, with no-go theorem implying that non-Abelian deformation of the tensor gauge symmetry is impossible in local theory with no other fields. Situation is even more complicated in six dimensions, as tensor field here is self-dual and arguments were given by Witten that superconformal action should not exist. Nevertheless, construction of a theory that captures at least some properties of the non-Abelian tensors is of interest, and many approaches have been proposed, with tensor hierarchies being the most conventional, local and Lorentz-covariant. The supersymmetric actions, constructed within the tensor hierarchy approach, however, suffer from instabilities as the kinetic term of the scalar fields is not positive-definite. In this talk, the manifestly supersymmetric action of the non-Abelian tensor is proposed that involves the positive-definite metric in the scalar sector. In the modified action, the self-dual equation of motion of the tensor field is induced by a composite Lagrange multiplier, which is not a component of a standard dynamical tensor multiplet. As a result, the constraint that enforces the gauge group to be non-compact, as in the usual tensor hierarchies, can be avoided. It is shown that for tensor field belonging to particular representations of $SU(3)$ and $SO(4)$ gauge groups, the Lagrangian multiplier is not dynamical. The talk is based on [N. Kozyrev, Supersymmetrizing the Pasti-Sorokin-Tonin action, JHEP 03 (2023) 223].

Speaker: Nikolay Kozyrev (BLTP JINR)

Kozyrev_Spb_2025.pdf

4:00 PM Limit law for eigenvalues of Jacobi Unitary Ensemble and skew Howe duality

We demonstrate that the limit density of eigenvalues of random matrices from Jacobi Unitary Ensemble (JUE) coincides with the transition probability for the limit shape of random Young diagrams with respect to the measure obtained from skew Howe duality. We discuss conjectural connection of asymptotics of correlation functions in these random ensembles.

Speaker: Anton Nazarov (SPbSU)

mqft.pdf

4:30 PM → 5:00 PM Coffee

5:00 PM → 6:20 PM Section B: Quantum field theory methods in elementary particle physics

5:00 PM The exotic state $Y(4230)$: molecular structure and strong decays

The hidden-charm strong decays of the exotic charmonium-like state $Y(4230)$, recently reported by the BESIII Collaboration, has been investigated in the framework of the covariant confined quark model. The state $Y$ has been interpreted as a four-quark state with molecular-type interpolating current. We evaluate the hidden-charm decay width of $Y$ into a vector and a scalar, with the latter decaying subsequently to a pair of charged pseudoscalar states [1]. The strong decay mode $Y\to\pi^{+} \pi^{-}$ has been studied by involving the both scalar resonances $f_0(500)$ and $f_0(980)$, considered quark-antiquark states, while the mode $Y \to K^{+} K^{-}$ - via $f_0(980)$. We have calculated the partial widths of the related strong decays and their branching ratio ${\cal BR}$, recently determined by the BESIII Collaboration. Note, the estimated branching ratio ${\cal BR} = 0.033 \pm 0.005$ is located near the experimental lower bound. The estimated branching ratio and calculated partial strong decay widths of the $Y(4230)$ state [1] do not contradict the latest experimental data and may be tested in future experiments.

[1]. Gurjav Ganbold and M. A. Ivanov, "Strong decays of charmonium-like state $Y(4230)$" // Eur. Phys. J. A 60:13 (2024).

Speaker: Ganbold Gurjav (Joint Institute for Nuclear Researches (JINR))

GurjavGanbold_MQFT2025_web.pdf

5:20 PM Resonant production of (milli)charged scalars in a timelike electromagnetic wave background

We study the possibility of resonant production of millicharged scalar particles by a timelike ($k^2>0$) electromagnetic wave, which can be experimentally obtained in plasma or in a medium with refractive index $n < 1$ (metamaterial). We show that the classical Klein-Gordon equation for the millicharged scalar field reduces to the Mathieu equation, which has exponentially growing solutions in certain areas of a parametric plane. We determine the area in momentum space of outgoing particles, for which the resonance occurs, and calculate the Floquet exponent which determines the rate of the resonance. Considering the cases of intense running and standing radio waves in a metamaterial with $n < 1$, we determine the projective bounds on the charge and mass of a millicharged scalar which can be obtained experimentally.

Speaker: Petr Satunin (INR RAS)

Millicharge_Res_MQFT_25_presentation-1.pdf

5:40 PM Holographic equation of state with strangeness for the study of the quark-gluon plasma evolution

At the beginning of the 21st century, a new phase of strongly interacting matter, known as the quark-gluon plasma (QGP), was established [1]. To study QGP formation in heavy-ion collisions, the solution of system of relativistic hydrodynamics equations with a specific equation of state (EoS) is typically employed. In light of difficulties for non-zero baryonic potentials within Lattice QCD, various holographic models based on the AdS/CFT duality have been proposed to obtain the QGP EoS from the thermodynamic properties of a corresponding black brane in AdS$_5$ [2].

In this work, we discuss possible phenomenological approaches for incorporating not only the baryon chemical potential but also the strangeness potential into holographic thermodynamics. The first method uses the established concept of a free quark gas with a specific symmetry generalization [3]. The second method employs a phenomenological hypothesis inspired by the thermodynamic dependencies of the hadron gas model [4]. We apply machine learning methods to address regression and optimization problems during the calibration of the model's free parameters using LQCD results for quark masses that approximate the physical values [5]. For practical applications in heavy-ion collision studies, the holographic EoS with strangeness is incorporated into the hydrodynamical packages MUSIC [6] and vHLLE [7].

To obtain final hadronic spectra, numerical simulations were conducted using the iEBE-MUSIC and SMASH-vHLLE frameworks; these additionally include packages for initial conditions, freeze-out, and a hadronic afterburner. The effect of the strangeness enabled EoS on the results is discussed.

The authors acknowledge Saint-Petersburg State University for a research project 103821868.

References:

1. J. Adams et al. (STAR Collab.), Nucl. Phys. A 757 102 (2005)

2. I. Aref’eva, K. Rannu, P. Slepov, Holographic anisotropic model for light quarks with confinement-deconfinement phase transition, J. High Energ. Phys. 2021, 90 (2021).

3. K.-il Kim, Y. Kim, S. H. Lee, Isospin Matter in AdS/QCD, Journal of the Korean Physical Society, 55 (2009), pp. 1381-1388

4. V. Vovchenko, H. Stoecker, Thermal-FIST: A package for heavy-ion collisions and hadronic equation of state, Comput. Phys. Commun. 244, 295 (2019)

5. M. Cheng et al., QCD equation of state with almost physical quark masses, Phys. Rev. D 77, 014511 (2008)

6. B. Schenke, S. Jeon, C. Gale, (3+1)D hydrodynamic simulation of relativistic heavy-ion collisions, Phys. Rev. C 82, 014903 (2010)

7. Iu. Karpenko, P. Huovinen, M. Bleicher, A 3+1 dimensional viscous hydrodynamic code for relativistic heavy ion collisions, Comput. Phys. Commun. 185 (2014), 3016

Speaker: Anton Anufriev (Saint Petersburg State University)

Anufriev_Kovalenko_MQFT2025.pdf

6:00 PM Searches for leptophobic B-bosons at the Troitsk Meson Factory (TiMoFey)

The talk will review the reconstruction project of the Troitsk Meson Factory (TiMoFey, INR RAS). One of the possible directions of its work is the search for light feebly interacting particles. For this purpose, it is planned to use the proton beams with kinetic energies of 423 MeV and 1300 MeV hitting a graphite target.

The talk will consider the model of the leptophobic B-boson interacting with the baryon current. We will discuss possible B-boson production channels and TiMoFey's expected sensitivity to visible decays of this particle.

The talk is based on arXiv:2508.01968.

Speaker: Ekaterina Kriukova (Institute for Nuclear Research of RAS & Institute of Theoretical and Mathematical Physics, MSU)

MQFT-Kriukova.pdf

5:00 PM → 6:20 PM Section D: Gravitation and cosmology

5:00 PM Non-singular solutions in Horndeski theories and their stability

In this talk, I will focus on non-singular solutions that can be realized within Horndeski theories, whose distinctive structure allows for controlled violations of energy conditions without introducing pathologies. I will review the typical stability challenges that arise at the level of linear perturbations and highlight how they constrain such solutions. Finally, I will discuss illustrative cosmological models that avoid an initial singularity and comment on their characteristic features.

Speaker: Victoria Volkova (INR RAS)

MQFT_2025_Volkova.pdf

5:20 PM Higher derivative scalar-vector-tensor theories viable for dark energy

We discuss latest results on Kaluza-Klein compactifications of Horndeski-type theories (beyond Horndeski and DHOST included). We show the subclass of such theories that obeys principal phenomenological constraints for dark energy models.

Speaker: Arina Shtennikova (INR RAS)

main.pdf

5:40 PM Self-tuning in beyond Horndeski theory

We investigate the possibility of addressing the cosmological constant problem through a self-tuning mechanism within the framework of beyond Horndeski theory. In particular, we propose a cosmological scenario in which self-tuning operates during inflation but switches off prior to reheating, while leaving behind the correct dark energy density. Furthermore, we explore the use of self-tuning in the context of Kaluza–Klein compactification of the five-dimensional Horndeski theory.

Speaker: Mikhail Sharov (INR RAS & ITMP MSU)

Sharov.pdf

6:00 PM Entanglement islands and black hole decay in regular dilaton gravity

We consider a class of two-dimensional dilaton gravity models with linear dilaton vacuum including Callan-Giddings-Harvey-Strominger (CGHS) model as the special case. General thermodynamic properties of black holes in such models are evaluated. We focus on the CGHS model and its modification with regular black holes as empty-space solutions characterized by ever-present finite curvature. We find generalized entanglement entropy blows-up for near-extremal regular black holes considered as remnants. That signalling a possible breakdown of the semiclassical approximation near the endpoint of evaporation. We conjecture that remnants are unstable and decay by quantum fluctuations into horizonless spacetimes. We give an estimate for the decay amplitude by using a semiclassical regularization method and propose a path to mitigate the unitarity loss problem.

Speaker: Maxim Fitkevich (INR RAS & MIPT)

mqft2025_talk_fitkevich.pdf

5:00 PM → 5:40 PM Section E: Integrable models, symmetries in QFT and quantum groups

5:00 PM Stability Properties of Bright Solitons in Two-dimensional CFT

We study non-topological bright solitons in two-dimensional conformal field theory. Our analysis shows that these solitons exhibit only zero modes, with no vibrational or decay excitations. This behavior is explained by examining a relativistic extension of the model, where conformal symmetry is weakly violated and decay modes appear. Thus, the restoration of conformal symmetry ensures the remarkable stability of the solutions.

Speaker: Eduard Kim (Moscow Institute of Physics and Technology)

Kim_Presentation.pdf

5:20 PM CFT-approach to Rotating Field Lumps in Attractive Potential

The importance of the realativistic corrections will be demonstrated for solitons in (2+1)-dimensional scalar theory with the conformal symmetry restoration in the non-relativistic limit. The conformal symmetry restoration affects the properties of solitons, such as their integral characteristics and stability.

Speaker: Yulia Galushkina (INR RAS)

Galushkina_mqft_2025.pdf

5:40 PM → 6:20 PM Section A: Mathematical methods in QFT

5:40 PM Thermal gravitational effective action in gauge theories and gravity

We calculate the nonlocal gravitational effective action for scalar field non-minimally coupled to gravity up to second order in curvature expansion at finite temperature and apply the result obtained to anomaly driven inflation scenario.

Speaker: Nikita Kolganov (LPI RAS & MIPT)

talk.pdf

6:00 PM Spectral form factors for curved spacetimes with horizon

In a recent series of papers, e.g. (Das, Krishnan, Kumar and Kundu, 2023), (Das, Garg, Krishnan and Kundu, 2023), (Das and Kundu, 2024), it was noted that the spectral form factor, defined for massless scalar field normal modes on the BTZ black hole background with a stretched horizon, exhibits the dip-ramp-plateau structure. This is exactly the same structure of the spectral form factor that observed for ensembles of random matrices. Normal modes are understood as the scalar field modes on the curved background with a Dirichlet boundary condition imposed at the horizon instead of the usual infalling boundary condition for quasi-normal modes. In this talk, we present the results where we have extended the analysis by considering massive scalar on the non-rotating and rotating BTZ backgrounds, the de Sitter case as well as the generalized spectral form factor that allows to take into account correlations between several levels, rather than two levels as in the standard definition.

Speaker: Vasilii Pushkarev (Steklov Mathematical Institute, Russian Academy of Sciences)

slides_Pushkarev.pdf

7:00 PM → 10:00 PM Conference dinner

Fri, October 10

10:00 AM → 11:20 AM Plenary Session

10:00 AM On the problem of studying the pole-running top-quark mass ratio in the Standard Model

The problem of essential scheme-dependence of the effects of the EW perturbative EW corrections to the ratio pole-running top quark mass is analysed in details. It is mentioned that the similar features may manifest itself in the cases of pole-running b- and c-quark masses. The less importance in these circumstances roles of the effects of higher order QCD corrections to the ratios of pole-MSbar running heavy quark masses are considered .

Speaker: Andrei Kataev (Institute for Nuclear Research of RAS)

Kataev-2025.pdf

10:40 AM Моdeling the interaction of continuous media with fundamental quantum fields.

The approach proposed by K. Symanzik for constructing quantum field models in inhomogeneous space-time is proposed to be used to describe the interaction of the basic fields of the theory of elementary particles with a continuous material medium. The main principles of constructing such models are formulated and examples of their application are given for studying the interaction of quantum electrodynamics fields with two-dimensional materials, analyzing the influence of the mechanisms of neutrino interaction with a material medium on the processes of their oscillations and astrophysical phenomena, as well as the most characteristic effects of photon interaction with an unstable continuous environment.

Speaker: Yury Pismak (Saint-Petersburg State University)

Vasiliev_ Pismak.pdf

11:20 AM → 11:40 AM Coffee

11:40 AM → 1:00 PM Plenary Session

11:40 AM Quantum electrodynamics in supercritical Coulomb field with heavy ions

The current status of testing QED in strong and supercritical Coulomb fields is considered. Special attention is paid to tests of QED in the supercritical Coulomb field. It is known that in slow collisions of two bare nuclei with the total charge number exceeding the critical value, $Z_1+Z_2 > Z_c =173$, the initially neutral vacuum can spontaneously decay into a charged vacuum and two positrons. The detection of spontaneous emission of positrons would be a direct proof of this fundamental phenomenon. However, the spontaneous emission of positrons is usually strongly masked by the dynamic (induced) emission of positrons, which is caused by a rapidly changing electromagnetic field created by colliding nuclei. For about three decades, it was believed that the vacuum decay can only be observed in collisions with nuclear sticking, when the nuclei are bound for a period of time due to nuclear forces. But to date, there is no evidence that nuclear sticking occurs in such collisions of heavy ions. However, in our recent papers [1-5] it has been shown that the vacuum decay can be observed without any sticking of the nuclei. This can be done by measuring the probabilities of the creation of positrons or positron spectra for a given set of nuclear trajectories. The results of this study will be presented in the talk.

This work was carried out with the financial support of the RSF grant No. 22-62-00004.

1. I.A. Maltsev, V.M. Shabaev, R.V. Popov, Y.S. Kozhedub, G. Plunien, X. Ma, Th. Stohlker, and D.A. Tumakov, Phys. Rev. Lett. 123, 113401 (2019)
2. R.V. Popov, V.M. Shabaev, D.A. Telnov, I.I. Tupitsyn, I.A. Maltsev, Y.S. Kozhedub, A.I. Bondarev, N.V. Kozin, X. Ma, G. Plunien, T. Stohlker, D.A. Tumakov, and V.A. Zaytsev, Phys. Rev. D 102, 076005 (2020).
3. R.V. Popov, V.M. Shabaev, I.A. Maltsev, D.A. Telnov, N.K. Dulaev, and D.A. Tumakov, Phys. Rev. D 107, 116014 (2023).
4. N.K. Dulaev, D.A. Telnov, V.M. Shabaev, Y.S. Kozhedub, I.A. Maltsev, R.V. Popov, and I.I. Tupitsyn, Phys. Rev. D 109, 036008 (2024).
5. N.K. Dulaev, D.A. Telnov, V.M. Shabaev, Y.S. Kozhedub, X. Ma, I.A. Maltsev, R.V. Popov, and I.I. Tupitsyn, Phys. Rev. D 111, 016018 (2025).

Speaker: Vladimir Shabaev

Shabaev_mqft_25.pdf

12:20 PM Threshold amplification of X(a,b)Y reactions: from muon-catalyzed fusion to electromagnetic formfactors of hyperons

Deviation of the cross section for the nuclear reaction X(a, b)Y from the Gamow formula due to an interaction additional to the Coulomb one in the entrance channel has been analyzed[1]. It is shown that the reaction cross section has an oscillating structure at low energies. If the maximum of the first oscillation is close to the threshold of the channel a+X, it has a resonance behavior[2]. To analyze the effect, simple relations between the period and the amplitude of the oscillations with parameters of the interaction have been derived. Specifically, they predict the cross-section oscillations of fusion (or muon-catalyzed fusion) reactions of the type X(a,b)Y for slow collisions between nuclei (a) and atomic target (X), as, for example, the reaction D(d,p)T between deuterons (d) and deuterium atoms (D)[2]. Similar behavior we also observed in muon-catalyzed fusion collisional reactions pμ + p and tμ + d[2].
Recently, we have extended the formalism developed in [2] for descriptions of the cross section of Λ-hyperon production in e+ e- collisions at high energies
$e^+ + e^- \rightarrow Λ^+_c + Λ^-_c$ ,
obtained by the BESIII Collaboration [3]. The application of this formalism to the analysis of electromagnetic form factors is also discussed.

[1] L.N. Bogdanova et. al. Sov. J. Nucl. Phys. 34, 662 (1981); Phys. Lett. B115, 171 (1982).
[2] V.S. Melezhik, Nucl. Phys. A550, 223 (1992)
[3] M. Ablikim et. al.Phys. Rev. Lett. 131, 191901 (2023)

Speaker: Vladimir Melezhik (BLTP JINR Dubna)

melezhik-MQFT-2025.pdf

1:00 PM → 2:30 PM Lunch

2:30 PM → 4:30 PM Section A: Mathematical methods in QFT

2:30 PM Form of axion in DFSZ models with $U(1)_{PQ}$ symmetry

Form of axion state in the DFSZ-I and DFSZ-II models are re-examined by diagonalizing the mass mixing matrix of $CP$-odd sector as well as applying $PQ$ mechanism to determine $PQ$ charges of particles that are used in general form of axion. In these models, $PQ$ charge of the singlet scalar is the only one parameter for $U(1)_{PQ}$ symmetry. Anomaly couplings of axion and axion-photon-photon couplings are studied in comparison with other Beyond Standard Models which also contain axion arise from $U(1)_{PQ}$ symmetry breaking. The contribution from scalar sector to the process $a \to \gamma \gamma$ is studied and shows significant values for axion searching experiments.

Speaker: Binh Vu (Bogoliubov Laboratory of Theoretical Physics, JINR)

MQFT2025.pdf

3:00 PM On a link between finite QFT formulation and the standard RG approach

The finite formulation of QFT, which is based on the system of the differential equations is discussed. This system of equations was previously formulated on the bare language; we show, that these equations can be re-formulated in a fully renormalized language. Next, it is demonstrated that under the certain conditions, the class of such finite renormalization prescriptions is equivalent to the classical renormalization group equation written in Callan-Symanzik-Ovsyannikov form. The possible presentation is based on the consideration ``On a link between finite QFT formulation and the standard RG approach’’ by Y. A. Ageeva and A. L. Kataev (in progress).

Speaker: Yulia Ageeva (INR RAS)

SPB_Link_RG_and_CS.pdf

3:30 PM N=2 AdS superspace and hypermultiplets

We present the harmonic superspace formulation of $\mathcal{N}=2$ hypermultiplet in AdS$_4$ background, starting from the proper realization of $4D$, $\mathcal{N}=2$ superconformal group $SU(2,2|2)$ on the analytic subspace coordinates. The key observation is that $\mathcal{N}=2$ $AdS_4$ supergroup $OSp(2|4)$ can be embedded as a subgroup in the superconformal group through introducing a constant symmetric matrix $c^{(ij)}$ and identifying the AdS supercharge as $\Psi^i_\alpha = Q^i_\alpha + c^{ik} S_{k\alpha}$, with $Q$ and $S$ being generators of the standard and conformal $4D$, ${\cal N}=2$ supersymmetries. Respectively, the AdS cosmological constant is given by the square of $c^{(ij)}$, $\Lambda = -6 c^{ij}c_{ij}$. We construct the $OSp(2|4)$ invariant hypermultiplet mass term by adding, to the coordinate AdS transformations, a piece realized as an extra $SO(2)$ rotation of the hypermultiplet superfield. It is analogous to the central charge $x_5$ transformation of flat $\mathcal{N}=2$ supersymmetry and turns into the latter in the super Minkowski limit. As another new result, we explicitly construct the superfield Weyl transformation to the $OSp(2|4)$ invariant AdS integration measure over the analytic superspace, which provides, in particular, a basis for unconstrained superfield formulations of the AdS$_4$-deformed $\mathcal{N}=2$ hyper Kahler sigma models. We find the proper redefinition of $\theta$ coordinates ensuring the AdS-covariant form of the analytic superfield component expansions.

E. Ivanov and N. Zaigraev, $\mathcal{N}=2$ AdS hypermultiplets in harmonic superspace, arXiv:2509.01406 [hep-th].

Speaker: Nikita Zaigraev (JINR, MIPT)

AdS2025.pdf

4:00 PM Chiral effective potential in 4D N = 1 supersymmetric gauge theories

We calculate the chiral effective superpotential in $4D$ $\mathcal{N}=1$ $SU(N)$ super Yang-Mills theory coupled to chiral matter in one- and two-loop approximations. It is found that the one-loop contribution to the chiral effective potential is always finite and is expressed in terms of a specific triangle integral. The two-loop contributions generated by purely chiral vertices turned out to be finite as well. The chiral effective potential stipulated by supergraphs with gauge superfield subgraphs is finite for the supergraphs with no divergent subgraphs. In the case of the finite $\mathcal{N}=2$ SYM theory, the two-loop chiral contributions to the effective action are significanlty simplified. The leading large $N$ behavior of the chiral effective superpotential in finite $\mathcal{N}=2$ super-Yang-Mills models with $SU(N)$ gauge symmetry is studied and it is shown that the exact form in the coupling constant of the chiral effective superpotential can be found.

Speaker: Alfiia Mukhaeva (BLTP JINR)

Mukhaeva.pdf

2:30 PM → 4:30 PM Section A: Mathematical methods in QFT

2:30 PM Off-diagonal functoriality and Mellin-Barnes integrals

Termwise integration of the asymptotic DeWitt expansion yields kernel expansions for a wide class of operator functions. These expansions involve the well-known HaMiDeW coefficients (this property is precisely the off-diagonal generalization of "functoriality") multiplied by some functions representable by Mellin-Barnes (MB) integrals. Off-diagonality, together with the use of the properties of MB integrals and the technique of integral transformations, provide great flexibility and power for this new approach.

Speaker: Wladyslaw Wachowski (Theory Department, Lebedev Physics Institute)

WachowskiMQFT2025.pdf

3:00 PM Schwarzian integrals calculus

We derive the general rules of functional integration in the theories of Schwarzian type,
thus completing the elaboration of Schwarzian functional integrals calculus.

The Schwarzian functional integrals has played a role in many areas of quantum physics.
In recent decades it has appeared in the quantum mechanical model of Majorana fermions with a random interaction (Sachdev-Ye-Kitaev model), the holographic
description of the Jackiw-Teitelboim dilaton gravity, the black hole physics, open string theory and some other models.

Functions
$$ \mathcal {E}_{\sigma }\left(u,\,v\right) =\left(\frac{2}{\pi\sigma^{2}}\right)^{\frac{3}{2}}\,\frac{1}{\sqrt{uv}}\,\exp\left\{\frac{2}{\sigma^{2}}\left(\pi^{2}-u-v\right) \right\} $$ $$ \times\int\limits_{0}^{+\infty}\,\exp\left\{-\frac{2}{\sigma^{2}}\left(2\,\sqrt{uv}\,\cosh\theta+\theta^{2}\right) \right\}\,\sin\left(\frac{4\pi\theta}{\sigma^{2}} \right)\,\sinh(\theta)\,d\theta $$
play a key role in finding Schwarzian functional integrals.

Talk is based on
V.V.Belokurov, E.T. Shavgulidze, (2020) Schwarzian functional integrals calculus. Journal of Physics A: Mathematical and Theoretical, 53 (48) 485201pp. doi:10.1088/1751-8121/abbd52

Speaker: Evgeniy Shavgulidze (Lomonosov Moscow University)

Shavgulidze_October2025_S.Peterburg.pdf

3:30 PM General formula for symmetry factors of Feynman diagrams

General formula for symmetry factors (S-factor) of Feynman diagrams containing fields with high spins is derived. We prove that symmetry factors of Feynman diagrams of well-known theories do not depend on spins of fields. In contributions to S-factors, self-conjugate fields and non self-conjugate fields play the same roles as real scalar fields and complex scalar fields, respectively. Thus, the formula of S-factors for scalar theories – theories include only real and complex scalar fields – works on all well-known theories of fields with high spins.

Speaker: Long Hoang

Hoang_Ngoc_Long_MQFT25.pdf

4:00 PM Higher derivatives regularization scheme for 6D, N = (1, 0) supersymmetric gauge theory in harmonic superspace

Using the harmonic superspace approach, we perform a comprehensive study of the structure of divergences in the higher-derivative $6D, {\cal N}=(1,0)$ supersymmetric Yang--Mills theory coupled to the hypermultiplet in the adjoint representation. The effective action is constructed in the framework of the superfield background field method with the help of $ {\cal N}=(1,0)$ supersymmetric higher-derivative regularization scheme which preserves all symmetries of the theory. The one-loop divergences are calculated in a manifestly gauge invariant and $6D, {\cal N}=(1,0)$ supersymmetric form hopefully admitting a generalization to higher loops. The $\beta$-function in the one-loop approximation is found and analyzed. In particular, it is shown that the one-loop $\beta$-function for an arbitrary regulator function is specified by integrals of double total derivatives in momentum space, like it happens in $4D, {\cal N}=1$ superfield gauge theories. This points to the potential possibility to derive the all-loop NSVZ-like exact $\beta$-function in the considered theory.

Speaker: Aleksandra Budekhina (BLTP JINR)

Budekhina_2025_MQFT.pdf

2:30 PM → 4:30 PM Section B: Quantum field theory methods in elementary particle physics

2:30 PM On scale and scheme dependence in cross sections of high-energy QED processes

The dependence of theoretical predictions for high-energy QED processes on factorization scale and scheme choices is studied. Examples for particular processes of Bhabha scattering, muon decay and electron-positron annihilation are presented.

Speaker: Andrej Arbuzov (BLTP JINR)

arbuzov_MQFT_2025.pdf

3:00 PM NRQED as an Effective Field Theory for the nonrelativistic bound states.

The nonrelativistic quantum electrodynamics (NRQED) formalism to the nonrelativistic bound state problem is developed. The next-to-leading order corrections ($mα^6$) to nonrelativistic binding energies are derived. The infinities which appear in the bound-state formalism at this order are discussed. We consider how higher-order corrections in the fine structure constant α, including contributions of order $mα^7$, can be obtained and calculated from the NRQED formalism.

Speaker: Vladimir Korobov (BLTP, JINR, Dubna, Russia)

NRQED25.pdf

3:30 PM Vacuum pair production and radiative processes in strong electromagnetic fields

In this talk, we will discuss the phenomenon of electron-positron pair production in strong electromagnetic fields and first- and second-order radiative processes. Main focus will be placed on the recent theoretical developments concerning a nonperturbative description of the above effects. We will briefly discuss modern theoretical approaches in quantum electrodynamics with unstable vacuum, as well as some novel results obtained in specific setups. Experimental prospects concerning strong-field QED will also be addressed.

Speaker: Ivan Aleksandrov

Aleksandrov_mqft_2025.pdf

4:00 PM Photon emission accompanying vacuum instability under the action of a quasi-constant electric field

The probability amplitudes of a photon emission from the vacuum accompanied by a created electron-positron pair or from a single-electron (positron) state in the presence of a constant electric field were considered earlier by Nikishov [Zh. Eksp. Teor. Fiz. 59, 1262 (1970)]. However, these amplitudes present a satisfactory description of the phenomenon of the emission in the case of not so strong field when the effect of the pair creation is tini. In the case of a strong field, one has to use a perturbation theory with respect to the radiative interaction for average values, which is quite different from the technique suitable for calculating amplitudes. Following a nonperturbative formulation of strong-field QED developed in our earlier works, we consider photon emission accompanying vacuum instability under the action of a quasi-constant strong electric field of finite duration T. We construct closed formulas for the total probabilities and study the photon emission by an electron and for the photon emission accompanying an electron-positron pair creation from a vacuum. We study angular and polarization distribution of the emission as well as emission characteristics in a high-frequency approximations with respect of 1/T. We see that the emission accompanying the pair creation from vacuum is distinguished by the fact of the cylindrical symmetry. It is a further development of the locally constant field approximation proposed in [Phys. Rev. D 95, 076013 (2017)].

Speaker: Sergei Gavrilov (Saint-Petersburg state forest technical university&ITMO University)

Gavrilov_mqft_2025.pdf

4:30 PM → 5:00 PM Coffee

5:00 PM → 6:20 PM Section A: Mathematical methods in QFT

5:00 PM Differential equations on Feynman integrals

We continue the development of a position space approach to equations for Feynman multi-loop integrals. The key idea of the approach is that unintegrated products of Greens functions in position space are still loop integral in momentum space. The natural place to start are the famous banana diagrams, which we explore in this paper. In position space, these are just products of n propagators. Firstly, we explain that these functions satisfy an equation of order 2n . These should be compared with Picard-Fuchs equations derived for the momentum space integral. We find that the Fourier transform of the position space operator contains the Picard-Fuchs one as a rightmost factor. The order of these operators is a special issue, especially since the order in momentum space is governed by degree in x in position space. For the generic mass case this factorization pattern is complicated and it seems like the order of the Fourier transformed position space operators is much bigger than that of the Picard-Fuchs. Furthermore, one may ask what happens if after factorization we take the Picard-Fuchs operators back into position space. We discover that the result is again factorized, with the rightmost factor being the original position space equation. We demonstrate how this works in examples and discuss implications for more sophisticated Feynman integrals.

Speaker: Maxim Reva (MIPT, ITEP)

Reva.pdf

5:20 PM Gravitational Wilson networks and Witten diagrams

The main topic of my talk is the correspondence between the gravitational Wilson line networks and Witten diagrams for massive scalar fields in AdS$_2$. I will show that Witten diagram can be expanded into a sum of gravitational Wilson line networks, where each term in the sum has distinct boundary behaviour. This expansion is similar to the conformal block expansion of conformal correlators and clearly shows the holographic correspondence between Witten diagrams in the bulk and conformal blocks at the boundary of AdS$_2$.

Speaker: Vladimir Khiteev (I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physical Institute RAS)

MQFT2025_Khiteev.pdf

5:40 PM All-loop effective potential in leading logarithmic approximation in non-renormalizable scalar field theories in curved space-time

In this work, we study the effective potential for non-renormalizable general and SO(N) symmetric scalar theories in curved space-time. We discuss a method for finding all-loop corrections in the leading logarithmic approximation, which incorporates the non-minimal coupling with gravity within the linear curvature approximation.

Using the Bogoliubov-Parasyuk theorem, we derive recurrence relations connecting different orders of loop correction contributions. Based on these relations, we obtain generalized renormalization group equations for the effective potential describing contributions on both flat and curved backgrounds. The developed approach is applicable to an arbitrary classical interaction potential. As an example, we analyze the simplest power-law potentials. It is shown that the obtained effective potentials can be considered in the theory of cosmological inflation. Finally, we calculate the cosmological parameters for these models and compare them with the observational data.

Speaker: Vladislav Filippov (JINR BLTP)

MQFT25_Filippov_1.pdf

MQFT25_Filippov_2.pdf

6:00 PM R-rule and effective potential in subleading logarithmic approximation in arbitrary non-renormalizable scalar field model

Effective potential in an arbitrary non-renormalizable scalar field model in subleading order is calculated. Based on BPHZ-renormalization and Bogoliubov-Parasiuk theorem it is found formalism to construct generalization of usual renormalization group equations. Application of this formalism leads to efficient way of calculation quantum contribution to effective potential whether renormalizable it is or not

Speaker: Ravil Iakhibbaev (JINR BLTP)

Iakhibbaev-MQFT25.pdf

5:00 PM → 6:20 PM Section B: Quantum field theory methods in elementary particle physics

5:00 PM $\mathcal{T}$, $\mathcal{P}$-odd electron-nucleon interaction via a Higgs-boson exchange

The search for $\mathcal{T}$- and $\mathcal{P}$-violating interactions, where $\mathcal{T}$ denotes time-reversal symmetry, and $\mathcal{P}$ denotes spatial parity, has been a central focus in fundamental physics for the past 75 years. Despite substantial progress in improving experimental limits on these interactions, theoretical predictions, even within the Standard Model (SM), remain highly uncertain.

This report examines various mechanisms responsible for $\mathcal{T}$- and $\mathcal{P}$-odd interactions. Notably, the electron electric dipole moment ($e$EDM), which violates both $\mathcal{T}$ and $\mathcal{P}$ symmetries, arises in the SM only at the four-loop level at the quark-gluon scale. Taking into account the Glashow-Iliopoulos-Maiani (GIM) mechanism, estimates of $e$EDM range from $10^{-44}$ to $10^{-50}$ $e\text{cm}$ [1–3]. At the hadronic level, the $e$EDM can arise at the one-loop level, with an estimated magnitude around $10^{-39}$$e \text{cm}$ [2].

In atomic systems, $\mathcal{T}$, $\mathcal{P}$-odd effects may also manifest as pseudoscalar-scalar electron-nucleon interactions. In our work, we initially proposed [4], and subsequently developed and evaluated taking into account the GIM mechanism [3], $\mathcal{T}$,~$\mathcal{P}$-odd exchange of the Higgs boson between the electron and the nucleus. The estimate derived in [3], recalculated in terms of an equivalent eEDM, yields a value $10^{-48}$$e \text{cm}$.

The literature contains various other models addressing $\mathcal{T}$- and $\mathcal{P}$-odd electron-nucleon interactions. The largest equivalent EDM reported to date, on the order of $10^{-35}$$e \text{cm}$, has been reported in [5], where the $\mathcal{T}$,~$\mathcal{P}$-odd exchange of $K$ mesons between electrons and nucleons was analyzed at the hadronic scale.

This work was supported by the Russian Science Foundation grant 24-72-10060.

References:

1. Pospelov M. and Ritz A. // Phys. Rev. D 89, 056006 (2014).

2. Yamaguchi Y. and Yamanaka N. // Phys. Rev. D 103, 013001 (2021).

3. Chubukov D.V. and Aleksandrov I.A. // Phys. Rev. D 111, 073011 (2025).

4. Chubukov D.V. and Labzowsky L.N. // Phys. Rev. A 93, 062503 (2016).

5. Ema Y., Gao T., and Pospelov M. // Phys. Rev. Lett. 129, 231801 (2022).

Speaker: Dmitry Chubukov

Chubukov_mqft_2025.pdf

5:20 PM Poly-vectors and the recovery effect

The Quantum Field Theory methods, related to the M-theory structures, are playing exceptional role in the modern science. They are commonly united in the general Gauge/Gravity correspondence. During the recent years of the related techniques' development, plenty of the general effects and their common features were recovered for the quantum field theories in the critical point, - conformal ones. It is natural to raise a question of the such theories' additional operators, changing their symmetries' structure. 
In the literature, they are classified by their action on the RG-flow of the initial quantum theory.  The marginal operators link the CFTs with various supersymmetry realisations, forming the so-called Conformal Manifold. The relevant ones are switching the trajectory of RG-flow, leading initial QFT to another critical point. The irrelevant additional operators are the ones, grabbing the initial CFT out of the critical point. Such a phenomenon is highly specific, as the Renormalisation Theory classifies generally them as non-renormalisable ones. There is an exceptional interest in exactly solvable irrelevant deformations, due to their deny of this statement. The most known example of them is $T\bar{T}$ deformation of the $\mathbb{R}^{1,1}$ CFTs, ruining their initial conformal symmetry and being solvable in terms of the $\beta/ \gamma$ system and CDD type factorisation of the S-matrix.
This project concerns phenomena of such deformations in the higher dimensional conformal theories, such as (3,3) $\mathbb{R}^{1,2}$ ABJM, (4,0) $\mathbb{R}^{1,3}$ SYM and (2,0) $\mathbb{R}^{1,5}$ SCFT. The main framework is the generalisation of $TsT$/$T\bar{T}$ correspondence, based on the features of the generalised Yang-Baxter deformations within proper poly-vectors. This talk concerns to reveal general properties of the deformed 11D and Type II SUGRA field equations' solutions, making them related to the generalisations of the Zamolodchikov solvable irrelevant deformation. 

References
1. L. McGough, M. Mezei, H. Verlinde, "Moving the CFT into the bulk with $T\bar{T}$", JHEP 04 (2018) 010.
2. Barakin S., Gubarev K., Musaev E. T. "Tri-vector deformations with external fluxes", Eur.Phys.J.C 84 (2024) 12, 1312
3. K. Gubarev, E. T. Musaev, and T. Petrov, "Polyvector deformations of Type IIB backgrounds", Eur. Phys. J. C 84 no. 10, (2024) 1085
4. Imeroni E., "On deformed gauge theories and their string/M-theory duals", JHEP 10 (2008) 026

Speaker: Sergei Barakin (ITMP, MIPT)

Barakin_mqft_2025.pdf

5:40 PM Runaway gravitational waves produced during first order phase transition in soft-wall holographic composite Higgs model

A bottom-up soft-wall holographic model is used to capture the non-perturbative dynamics of a composite Higgs sector undergoing a first-order phase transition. Employing a controlled perturbative expansion in the dual 5D theory, we obtain estimations of bubble nucleation rates and other parameters of phase transition. This semi-analytic approach yields a prediction for the resulting gravitational-wave spectrum in the runaway scenario, and identifies where thin-wall and quasiclassical methods remain reliable.

Speaker: Andrey Shavrin (Saint Petersburg State University)

GW_slides_MQFT_25-2.pdf

6:00 PM Green's functions scattering approach in the calculation of the Casimir-Polder potential in systems with Chern-Simons boundary layers

The report presents a generalization of the Green’s function method for the scattering problem, allowing for the mixing of electromagnetic polarizations upon reflection from planar interfaces with Chern–Simons (CS) boundary layers. The developed approach makes it possible to systematically derive the Casimir-Polder potential for systems with such boundaries.

The formula for the Casimir–Polder interaction between an anisotropic atomic dipole and a single CS boundary layer at the surface of a homogeneous dielectric half-space is obtained. This result is further generalized to the case of two parallel dielectric half-spaces with CS boundary layers. For the system of two CS layers in vacuum, the Casimir-Polder potential is expressed in terms of special functions.

Fundamentally new results are the prediction and analysis of new P-odd three-body vacuum effects occurring between two parallel CS layers and a neutral atom in the ground state. It is shown that these effects depend on the orientation of the Chern-Simons layers.

The results obtained indicate the possibility of observing P-odd vacuum effects in experiments with neutral atoms.

Speaker: Arseny Sidelnikov (Saint Petersburg State University)

Sidelnikov_mqft_2025.pdf

5:00 PM → 6:20 PM Section B: Quantum field theory methods in elementary particle physics

5:00 PM Correlations of fluctuations and phase transitions in QC$_2$D

Based on numerical simulation of two-color QCD in lattice regularization, correlations between fluctuations of the quark condensate, the net-quark number density, and the Polyakov loop are estimated.
For the pion mass $\sim 700$~MeV, there is a significant correlation at temperatures of $200-320$~MeV, which indicates a connection between the dynamics of chiral symmetry restoration and confinement at zero baryon number density.
It is also shown that, with an increase in the baryon chemical potential, this correlation disappears giving some evidence for the difference in the mechanisms of the chiral transition and the transition to deconfinement at $\mu_B > T_c$.

Speaker: Roman Rogalyov (IHEP)

rogalyov.pdf

5:20 PM Mixed inhomogeneous phase in rotating gluon plasma within lattice simulations

Using first-principle numerical simulations, we find a new spatially inhomogeneous phase in rotating gluon plasma. This mixed phase simultaneously contains regions of both confining and deconfining states in thermal equilibrium. The location of the spatial transition between the two phases is determined by the local critical temperature. We measure the local critical temperature as a function of angular velocity and radius for a full imaginary rotating system and within a local thermalization approximation, and find good agreement between these approaches. An analytic continuation of our results to the domain of real angular frequencies indicates a profound violation of the Tolman-Ehrenfest law in the vicinity of the phase transition, with the confining (deconfining) phase appearing farther from (closer to) the rotation axis.

Speaker: Artem Roenko (BLTP, JINR)

roenko_mqft25.pdf

5:40 PM Gluodynamics in accelerated frames using lattice simulation

We investigate the properties of SU(3) gluon plasma at high temperature under acceleration using lattice simulations in Rindler spacetime. Our results reveal a spatial crossover transition from confinement to deconfinement opposite to the direction of acceleration, consistent with the Tolman-Ehrenfest (TE) law. Using this law, we renormalize the Polyakov loop in Rindler space. Additionally, we observe that the transition width and peak diminish as acceleration increases.

Speaker: Jayanta Dey (BLTP JINR)

Jayanta_MQFT-2025.pdf

6:00 PM Lattice study of total momentum and free energy of rotating gluon plasma

In this report we present the results of our study of rotating gluodynamics. In particular, we carry out lattice calculation of total angular momentum of rotating gluodynamics for various temperatures and angular velocities within local thermalization approximation. In this approximation, instead of simulating the full action, we use the action with the coefficients being fixed at some distance from the axis of rotation. The results for the total gluon momentum are used to construct the free energy of rotating gluon plasma.

Speaker: Dmitrii Sychev (BLTP JINR, MIPT)

Sychev_presentation_2025oct10_v1.pdf