arXiv subjects

V. Skokov

Publications and source records attributed to V. Skokov.

At least 19 recordsLinked to original sources

arXiv2026

Precision QCD with the Electron-Ion Collider

This document summarizes the discussions at the program "Precision QCD with the Electron Ion Collider", held from May to June 2025 at the Institute for Nuclear Theory (INT) at the University of Washington. The program was co-sponsored by the INT and by the Center for Frontiers in Nuclear Science (CFNS, Stony Brook University). Over its five-week duration it brought together about 70 theorists, experimentalists and computer scientists all interested in the physics program at the future Electron Ion Collider in preparation at Brookhaven National Laboratory. Key topics at the program were: higher-order perturbative-QCD calculations and techniques; nuclear structure and tomography; comparisons of phenomenological and lattice determinations of parton distribution functions; identification of signature observables for saturated gluons; assessment of the importance of AI techniques for EIC studies and detector development.

hep-ph↗

arXiv2021

Transasymptotics and hydrodynamization of the Fokker-Planck equation for gluons

We investigate the non-linear transport processes and hydrodynamization of a system of gluons undergoing longitudinal boost-invariant expansion. The dynamics is described within the framework of the Boltzmann equation in the small-angle approximation. The kinetic equations for a suitable set of moments of the one-particle distribution function are derived. By investigating the stability and asymptotic resurgent properties of this dynamical system, we demonstrate, that its solutions exhibit a rather different behavior for large (UV) and small (IR) effective Knudsen numbers. Close to the forward attractor in the IR regime the constitutive relations of each moment can be written as a multiparameter transseries. This resummation scheme allows us to extend the definition of a transport coefficient to the non-equilibrium regime naturally. Each transport coefficient is renormalized by the non-perturbative contributions of the non-hydrodynamic modes. The Knudsen number dependence of the transport coefficient is governed by the corresponding renormalization group flow equation. An interesting feature of the Yang-Mills plasma in this regime is that it exhibits transient non-Newtonian behavior while hydrodynamizing. In the UV regime the solution for the moments can be written as a power-law asymptotic series with a finite radius of convergence. We show that radius of convergence of the UV perturbative expansion grows linearly as a function of the shear viscosity to entropy density ratio. Finally, we compare the universal properties in the pullback and forward attracting regions to other kinetic models including the relaxation time approximation and the effective kinetic Arnold-Moore-Yaffe (AMY) theory.

hep-ph↗

arXiv2019

Saturation corrections to dilute-dense particle production and azimuthal correlations in the Color Glass Condensate

We perform a numerical study of higher order saturation corrections to the dilute-dense approximation for multi-particle production in high-energy hadronic collisions in the framework of the Color Glass Condensate. We compare semi-analytical results obtained by performing a leading order expansion in the dilute field of the projectile with numerical simulations of the full Classical Yang-Mills dynamics for a number of phenomenologically relevant observables. By varying the saturation momentum of the target and the projectile, we establish the regime of validity of the dilute-dense approximation and assess the magnitude and basic features of higher order saturation corrections. In particular, we find that dilute-dense approximation faithfully reproduces dense-dense results if restricted to the range of its validity.

hep-ph↗

arXiv2016

Volume fluctuations and higher order cumulants of the net baryon number

We consider the effect of volume fluctuations on cumulants of the net baryon number. Based on a general formalism, we derive universal expressions for the net baryon number cumulants in the presence of volume fluctuations with an arbitrary probability distribution. The relevance of these fluctuations for the baryon-number cumulants and in particular for the ratios of cumulants is assessed in the Polyakov loop extended quark-meson model within the functional renormalization group. We show that the baryon number cumulants are generally enhanced by volume fluctuations and that the critical behavior of higher order cumulants may be modified significantly.

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arXiv2013

Comments About the Electromagnetic Field in Heavy-Ion Collisions

In this short article we discuss the properties of electromagnetic fields in heavy-ion collisions and consequences for observables. We address quantitatively the issue of the magnetic field lifetime in a collision including the electric and chiral magnetic conductivities. We show that for reasonable parameters, the magnetic field created by spectators in a collision is not modified by the presence of matter. Based on this, we draw definite conclusions on observed effects in heavy-ion collisions.

hep-ph↗

arXiv2011

Phase diagram in an external magnetic field beyond a mean-field approximation

The phase structure of the Polyakov loop-extended chiral quark-meson model is explored in a nonperturbative approach, beyond a mean-field approximation, in the presence of a magnetic field. We show that by including meson fluctuations one cannot resolve the qualitative discrepancy on the dependence of the crossover transition temperature in a non-zero magnetic field between effective model predictions and recent lattice results (arXiv:1111.4956).We compute the curvature of the crossover line in the T - μ_B plane at a non-zero magnetic field and show that the curvature increases with increasing magnetic field. On the basis of QCD inequalities, we also argue that, at least in the large Nc limit, a chiral critical end point and, consequently, a change from crossover to a first-order chiral phase transition are excluded at zero baryon chemical potential and non-zero magnetic field.

hep-ph↗

arXiv2011

Net-charge probability distributions in heavy ion collisions at chemical freeze-out

We explore net charge probability distributions in heavy ion collisions within the hadron resonance gas model. The distributions for strangeness, electric charge and baryon number are derived. We show that, within this model, net charge probability distributions and the resulting fluctuations can be computed directly from the measured yields of charged and multi-charged hadrons. The influence of multi-charged particles and quantum statistics on the shape of the distribution is examined. We discuss the properties of the net proton distribution along the chemical freeze-out line. The model results presented here can be compared with data at RHIC energies and at the LHC to possibly search for the relation between chemical freeze-out and QCD cross-over lines in heavy ion collisions.

hep-ph↗

arXiv2011

Non-perturbative dynamics and charge fluctuations in effective chiral models

We discuss the properties of fluctuations of the electric charge in the vicinity of the chiral crossover transition within effective chiral models at finite temperature and vanishing net baryon density. The calculation includes non-perturbative dynamics implemented within the functional renormalization group approach. We study the temperature dependence of the electric charge susceptibilities in the linear sigma model and explore the role of quantum statistics. Within the Polyakov loop extended quark-meson model, we study the influence of the coupling of quarks to mesons and to an effective gluon field on charge fluctuations. We find a clear signal for the chiral crossover transition in the fluctuations of the electric charge. Accordingly, we stress the role of higher order cumulants as probes of criticality related to the restoration of chiral symmetry and deconfinement.

hep-ph↗

arXiv2011

Mapping the phase diagram of strongly interacting matter

We employ a conformal mapping to explore the thermodynamics of strongly interacting matter at finite values of the baryon chemical potential $μ$. This method allows us to identify the singularity corresponding to the critical point of a second-order phase transition at finite $μ$, given information only at $μ=0$. The scheme is potentially useful for computing thermodynamic properties of strongly interacting hot and dense matter in lattice gauge theory. The technique is illustrated by an application to a chiral effective model.

hep-ph↗

arXiv2011

Charge fluctuations in chiral models and the QCD phase transition

We consider the Polyakov loop-extended two flavor chiral quark--meson model and discuss critical phenomena related with the spontaneous breaking of the chiral symmetry. The model is explored beyond the mean-field approximation in the framework of the functional renormalisation group. We discuss properties of the net-quark number density fluctuations as well as their higher cumulants. We show that with the increasing net-quark number density, the higher order cumulants exhibit a strong sensitivity to the chiral crossover transition. We discuss their role as probes of the chiral phase transition in heavy-ion collisions at RHIC and LHC.

hep-ph↗

arXiv2011

Net-proton probability distribution in heavy ion collisions

We compute net-proton probability distributions in heavy ion collisions within the hadron resonance gas model. The model results are compared with data taken by the STAR Collaboration in Au-Au collisions at sqrt(s_{NN})= 200 GeV for different centralities. We show that in peripheral Au-Au collisions the measured distributions, and the resulting first four moments of net-proton fluctuations, are consistent with results obtained from the hadron resonance gas model. However, data taken in central Au-Au collisions differ from the predictions of the model. The observed deviations can not be attributed to uncertainties in model parameters. We discuss possible interpretations of the observed deviations.

hep-ph↗

arXiv2011

Fluctuations as probe of the QCD phase transition and freeze-out in heavy ion collisions at LHC and RHIC

We discuss the relevance of higher order moments of net baryon number fluctuations for the analysis of freeze-out and critical conditions in heavy ion collisions at LHC and RHIC. Using properties of O(4) scaling functions, we discuss the generic structure of these higher moments at vanishing baryon chemical potential and apply chiral model calculations to explore their properties at non-zero baryon chemical potential. We show that the ratios of the sixth to second and eighth to second order moments of the net baryon number fluctuations change rapidly in the transition region of the QCD phase diagram. Already at vanishing baryon chemical potential they deviate considerably from the predictions of the hadron resonance gas model which reproduce the second to fourth order moments of the net proton number fluctuations at RHIC. We point out that the sixth order moments of baryon number and electric charge fluctuations remain negative at the chiral transition temperature. Thus, they offer the possibility to probe the proximity of the thermal freeze-out to the crossover line.

hep-ph↗

arXiv2010

The influence of fluctuations on thermodynamics near chiral phase transition

We discuss the influence of fluctuations on thermodynamics near the chiral phase transition within Polyakov loop extended quark--meson model based on the functional renormalization group (FRG) method. We include the gluon fields in the FRG flow equation self-consistently on the mean-field level. We focus on the properties of the phase diagram and net-baryon number fluctuations.

hep-ph↗

arXiv2010

The renormalization group and quark number fluctuations in the Polyakov loop extended quark-meson model at finite baryon density

Thermodynamics and the phase structure of the Polyakov loop-extended two flavors chiral quark--meson (PQM) model is explored beyond the mean-field approximation. The analysis of the PQM model is based on the functional renormalization group (FRG) method. We formulate and solve the renormalization group flow equation for the scale-dependent thermodynamic potential in the presence of the gluonic background field at finite temperature and density. We determine the phase diagram of the PQM model in the FRG approach and discuss its modification in comparison with the one obtained under the mean-field approximation. We focus on properties of the net-quark number density fluctuations as well as their higher moments and discuss the influence of non-perturbative effects on their properties near the chiral crossover transition. We show, that with an increasing net-quark number density the higher order moments exhibit a peculiar structure near the phase transition. We also consider ratios of different moments of the net-quark number density and discuss their role as probes of deconfinement and chiral phase transitions.

hep-ph↗

arXiv2010

Vacuum fluctuations and the thermodynamics of chiral models

We consider the thermodynamics of chiral models in the mean-field approximation and discuss the relevance of the (frequently omitted) fermion vacuum loop. Within the chiral quark-meson model and its Polyakov loop extended version, we show that the fermion vacuum fluctuations can change the order of the phase transition in the chiral limit and strongly influence physical observables. We compute the temperature-dependent effective potential and baryon number susceptibilities in these models, with and without the vacuum term, and explore the cutoff and the pion mass dependence of the susceptibilities. Finally, in the renormalized model the divergent vacuum contribution is removed using the dimensional regularization.

hep-ph↗

arXiv2010

Meson fluctuations and thermodynamics of the Polyakov loop extended quark-meson model

Thermodynamics and the phase structure of the Polyakov loop-extended two flavor chiral quark-meson model (PQM) are explored. The analysis of the PQM model is based on the functional renormalization group (FRG) method. An appropriate truncation of the effective action with quarks coupled to background gluonic fields is introduced. Within this scheme, we derive the renormalization group flow equation for the scale-dependent thermodynamic potential at finite temperature and density in the presence of a symmetry breaking external field. The influence of fluctuations and of the background gluon field on the properties of net-quark number density fluctuations and their higher moments is explored. We study the dependence of the kurtosis of quark number fluctuations on the pion mass and show that, in the presence of a symmetry breaking term, the fluctuations lead to a smoothing of observables near the crossover transition.

hep-ph↗

arXiv2009

Enhanced heavy quark-pair production in strong SU(2) color field

Non-perturbative charm and bottom quark-pair production is investigated in the early stage of heavy ion collisions. Following our earlier works, the time-dependent study is based on a kinetic description of fermion-pair production in strong non-Abelian fields. We introduce time-dependent chromo-electric external field with a pulse-like time evolution, which simulates the overlap of two colliding heavy ions. The calculations is performed in a SU(2) color model with finite current quark masses. Yields of heavy quark-pairs are compared to the ones of light and strange quark-pairs. We show that the small inverse duration time of the field pulse determines the efficiency of the quark-pair production. Thus we do not see the expected suppression for heavy quark production, as follows from the Schwinger formula for constant field, but rather an enhanced heavy quark production at ultrarelativistic energies. We convert pulse duration time-dependent results into collisional energy dependence and introduce flavour-dependent energy string tensions, which can be used in string based model calculations at RHIC and LHC energies.

hep-ph↗

arXiv2009

Estimate of the magnetic field strength in heavy-ion collisions

Magnetic fields created in the noncentral heavy-ion collision are studied within a microscopic transport model, namely the Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). Simulations were carried out for different impact parameters within the SPS energy range ($E_{lab} = 10 - 158 A$ GeV) and for highest energies accessible for RHIC. We show that the magnetic field emerging in heavy-ion collisions has the magnitude of the order of $eB_y \sim 10^{-1} m_π^2$ for the SPS energy range and $eB_y \sim m_π^2$ for the RHIC energies. The estimated value of the magnetic field strength for the LHC energy amounts to $eB_y \sim 15 m_π^2$.

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