Fundamental Interactions of Fields and Particles

Participating Countries and International organizations:

Argentina, Armenia, Azerbaijan, Belarus, Bulgaria, Canada, CERN, Chile, China, Czech Republic, Finland, France, Georgia, Germany, Hungary, ICTP, India, Italy, Japan, Kazakhstan, Mexico, Mongolia, New Zealand, Norway, Portugal, Poland, Republic of Korea, Russia, Serbia, Slovakia, Spain, Sweden, Switzerland, USA, Ukraine, United Kingdom, Uzbekistan, Vietnam.

Issues addressed and main goals of research:

The main aim of the research within the theme is the construction of theoretical models and their application to the description of properties of elementary particles and their interactions. This research includes the following directions of activity.
The development of quantum field theory formalism in gauge and supersymmetric theories. Construction and investigation of the models of particle physics beyond the Standard Model. Theoretical support of experiments at the Large Hadron Collider on the search of new physics and the study of the properties of the Higgs boson. Calculation of radiative corrections to the processes of particle creation within the Standard Model and its extensions. Investigation of neutrino properties and neutrino oscillations. Investigation of the hadron properties within quantum chromodynamics and phenomenological quark models. Study of the hadron spin structure with the help of generalized and transverse momentum dependent parton distributions and theoretical support of NICA/SPD program. Study of heavy quark properties and exotic hadrons. Lattice simulations for obtaining nonperturbative results in gauge theories. Investigation of dense hadronic matter and theoretical support of the MPD/NICA program. Theoretical support of a wide range of current and future experiments at JINR, IHEP, CERN, GSI, JLab and other physics centers.

Expected main results in the current year:

• Study of non-supersymmetric gauge theories of higher dimensions, derivation of the generalized renormalization group equations, and finding of the high-energy behavior of scattering amplitudes in these theories.

Investigation of the renormalization scheme dependence of scattering amplitudes in supersymmetric gauge theories of higher dimensions.

Calculation of the spectral density for a 3-loop photon polarization operator in QED and QCD with account for 4 particle massive cuts.

Investigation of the renormalization group relations for the higher-order perturbative expansion coefficients of the hadronic vacuum polarization function as well as the relevant expressions for the coefficients incorporating the contributions of the π²-terms in the perturbative expansion of the R-ratio of electron-positron annihilation into hadrons.

Development of methods for solving the quantum spectral curve equations in the N=4 supersymmetric Yang–Mills theories and Aharony-Bergman-Jafferis-Maldacena models. Construction of algorithmic solutions for universal anomalous dimensions of the twist 2 operators in 8 and 6 loop approximations, respectively.

Development of the theory of transverse momentum dependent parton densities with the application to heavy-quark production.

Construction of the longitudinal structure function F_L(x,Q²) at small x obtained from the Froissart-bounded parametrization of F₂(x,Q²).

Large Bjorken x variable resummation in QCD non-singlet data analysis of deep inelastic scattering on a fixed target.

• Numerical optimization for the perturbative series using the renormalization group (RG) in QCD and truncated Mellin moments approach. Application to the deep-inelastic scattering sum rules and comparison with the experimental data.

Calculation of lepton-pair production in exclusive hadron processes with taking into account the electromagnetic contribution.

Calculation of hadron spin structure effects in the framework of transverse momentum dependent parton densities in a proton to support the NICA-SPD program.

Investigation of electromagnetic and gravitational interactions of twisted particle states and analysis of possibilities of their production in heavy-ion collisions.

Calculation of different form factors, which parametrize the transition of a pion-nucleon mode into the virtual photon and nucleon within the QCD light-cone sum rules, including the twist-3, twist-4 contributions and the coupling constant corrections.

Determination of the properties of the long-range hadron potential, which define peculiar properties of the differential cross sections of proton-proton elastic scattering obtained at the LHC. Investigation and determination of the energy dependence of new effects detected in the experimental data by the TOTEM Collaboration at an energy of 13 TeV.

Calculation of the helicity amplitudes of proton-proton scattering in the framework of the High Energy General Structure model with taking into account the nucleon structure for description of the polarization effects at NICA energies.

Investigation of the influence of quantum anomalies on transport phenomena in a vortical relativistic fluid containing elementary particles with spin one and polarization caused by these phenomena; calculation of anomalous currents of particles with spin one.

Сomparative analysis of the results for pion transition and electromagnetic form factors in the low and (or) moderate energy regime experiments.

Evaluation of radiative corrections to distribution amplitudes of (pseudo)scalar and (longitudinal and transverse) vector mesons at N²LO in the large-𝛽₀ approximation for the perturbative part of the QCD sum rules.

Development of the efficient Monte Carlo integration and event generation method based on machine learning algorithms using the existing Tensorflow and Keras machine learning libraries.

Test of leptonic universality for the convexity parameter in semileptonic meson and baryon decays independent of lepton mass and form factor effects.

Calculations of nonleptonic two-particle decays of charmed baryons including the quark diagrams topologically different from tree diagrams.

Improvement of the values of the fundamental constants of atomic physics (Rydberg constant, the ratio of the proton to electron masses) and imposing of more stringent restrictions on the interaction potentials of the "fifth" force using the effective field theory "Nonrelativistic quantum electrodynamics" and high precision spectroscopy of  HD⁺, antiproton helium and molecular ion H₂⁺.

• Development of empirical an approach for calculating the cross sections of charged-current quasielastic (CCQE) and CCQE-like interactions of neutrinos and antineutrinos with nuclei. An extensive comparison of calculations with the earlier and modern accelerator CCQE and CCQE-like data for different nuclear targets in a wide energy range.
  
  Implementation of the SuSAM* model into the GENIE neutrino event generator.

Investigation of the reactor antineutrino anomaly (RAA) within the framework of a quantum field theoretical approach to neutrino oscillations. Analysis of the early reactor data and most recent results from the new experiments such as PROSPECT, Stereo, NEUTRINO-4, and DANSS.

Description of differential distributions of semi-leptonic modes of tau-lepton decays studied at modern and future colliders with taking into account meson-meson interactions.

Construction of high-precision theoretical predictions for the main processes of electron-positron annihilation taking into account the initial beam polarization under the conditions of future colliders including the Super Charm-Tau Factory, ILC and FCC-ee.

• Description of the structure of quark and hybrid matter in neutron stars using the extended sigma model.
  
  Study of the properties of the low-temperature high-density equation of state from multi-messenger Astronomy of compact stars and their mergers:  indications the existence of a third family of compact stars (mass twins) and implications for the existence of a critical endpoint in the QCD phase diagram; Bayesian analyses of new observables from GW170817, GW190814 and NICER for different mixed phase constructions of the hybrid quark-hadron EoS; question of the onset of deconfinement in the mass-radius diagram and in the EoS,  hybrid EoS regarding their supernova explodability property.

Development of self-consistent approximations to dilute heated hadronic matter in application to heavy ion collisions and supernova matter. Investigation of the influence of in-medium pion effects, magnetic field and rotation on the equation of state of heated hadron matter.

Calculation of the mass gap in the fermion spectrum and study of its dependence on the chemical potential in QCD-like theories by means of lattice simulations.

Study of the QCD equation of state in the external magnetic field and at nonzero baryon density within lattice simulation.

Study of a chiral magnetic wave in quark-gluon plasma in an external magnetic field using lattice simulation with dynamical quarks and physical mass of the π-meson.

Investigation of the finite size effects in the effective potential of gluodynamics for self-dual and chromomagnetic background gluon fields within lattice simulations under various boundary conditions.

Study of spectral functions of quark bound states within the effective quark-meson model by means of the functional renormalisation group. Application of these spectral functions for calculation of transport coefficients in the effective model for both massive bare quarks and the chiral limit of massless quarks.

Development of a unified quark-hadron equation of state satisfying the constraints of Lattice QCD to study the hadron resonance gas with the Mott dissociation and quark confinement mechanism, application to a system with high baryon and isospin densities and prediction of critical endpoint location(s) in application to relativistic heavy ion experiments as well as compact star astrophysics.

Inclusion of event-by-event effects in the HydHSD hybrid model of heavy ion collisions, which combines viscous hydrodynamics of second order with the HSD/PHSD kinetic model, for a detailed study of an elliptic flow.

Update of the event generator based on the model of three-fluid dynamics (3FD). This updated version will be more suitable for simulations of heavy-ion collisions at BM@N and MPD-NICA energies. Study of production of nuclear fragments in heavy-ion collisions, formation and time evolution of collective flow in heavy-ion collisions within the updated THESEUS generator.

Study of the origin and applications of the Tsallis non-extensive statistics describing systems with long-range correlation in a more detailed manner by relaxing the factorization approximation. Investigation of the propagation of nonlinear waves inside quark-gluon plasma medium following the Tsallis-like momentum distribution for realistic phenomenological problems of relativistic heavy ion physics. 

Collaboration