arXiv subjects

V. V. Braguta

Publications and source records attributed to V. V. Braguta.

At least 19 recordsLinked to original sources

arXiv2026

Spatially inhomogeneous confinement-deconfinement phase transition in rotating QGP

Using first-principles numerical simulations, we find a new spatially inhomogeneous phase in a rotating gluon plasma. This mixed phase simultaneously contains regions of both confining and deconfining states in thermal equilibrium, separated by a spatial transition. The position of the boundary between the two phases is determined by the local critical temperature. We calculate the critical temperature of the local transition as a function of angular velocity and radius for a full (imaginary) rotating system and within a local thermalization approximation, and find an excellent agreement between these approaches. An analytic continuation of the results to the domain of real angular frequencies indicates that the confinement phase localizes at the periphery of the rotating system and the deconfinement phase appears closer to the rotation axis. We argue that the anisotropy of the gluon action in the curved co-rotating background can quantitatively explain the remarkable property that the spatial structure of this inhomogeneous phase disobeys the picture based on a straightforward implementation of the Tolman-Ehrenfest law. We also perform the first lattice simulation of rotating $N_f=2$ QCD which confirms that a similar picture is expected for theory with dynamical quarks.

hep-lat↗

arXiv2025

On the origin of mixed inhomogeneous phase in vortical gluon plasma

Recently, lattice simulations of SU(3) Yang-Mills theory revealed that rotating hot gluon matter in thermal equilibrium possesses a novel inhomogeneous phase consisting of the deconfinement phase located in the center region, which is spatially separated from the confinement phase in the periphery. This inhomogeneous two-phase structure is also expected to be produced by vorticity in quark-gluon plasma formed in non-central relativistic heavy-ion collisions. We show that its vortical properties are determined by two types of couplings of the angular velocity to the gluon fields: a linear coupling to the mechanical angular momentum of gluons and a quadratic ``magnetovortical'' coupling to a chromomagnetic component. We demonstrate numerically that the distinctive inhomogeneous structure of the vortical (quark-)gluon plasma is determined by the latter, while the former plays only a subleading role. We argue that the anisotropy of the gluonic action in the curved co-rotating background can quantitatively explain the remarkable property that the spatial structure of this inhomogeneous phase disobeys the picture based on a straightforward implementation of the Tolman-Ehrenfest law. We also support our findings with Monte Carlo simulations of Yang-Mills plasma at the real-valued angular frequency, which take into account only the magnetic part of the action.

hep-lat↗

arXiv2025

Chiral and deconfinement thermal transitions at finite quark spin polarization in lattice QCD simulations

We study the effect of finite spin quark density on the chiral and deconfinement thermal crossovers using numerical simulations of lattice QCD with two dynamical light quarks. The finite spin density is introduced by the quark spin potential in the canonical formulation of the spin operator. We show that both chiral and deconfinement temperatures are decreasing functions of the spin potential. We determine the parabolic curvatures of crossover temperatures in a limit of physical quark masses.

hep-lat↗

arXiv2024

Electrical conductivity of the Quark-Gluon Plasma in the presence of strong magnetic fields

We compute the electrical conductivity of the strongly interacting medium in the presence of strong magnetic background fields, $eB=4,9~GeV^2$, and for different values of the temperature, both in the confined and in the deconfined Quark-Gluon Plasma (QGP) phase. The conductivity is obtained from the Euclidean lattice time correlator of the electrical current, computed on gauge configurations sampled from Monte-Carlo simulations of an improved staggered discretization of $N_f = 2+1$ QCD. We perform the inverse Laplace transform of the correlator adopting a recently-proposed version of the standard Backus--Gilbert procedure for the inversion. The results obtained in the QGP phase show a sizable enhancement of the conductivity in the direction parallel to the magnetic field, as well as a suppression in the direction orthogonal to it. Such enhancement could be attributed to the manifestation of the Chiral Magnetic Effect (CME): following this guess, we extract the behaviour of the relaxation time of this process, extrapolate it to the continuum limit and compare it to previous results, finding it lower than expected in the explored range of temperatures.

hep-lat↗

arXiv2024

QCD Equation of State at nonzero baryon density in external magnetic field

This paper is devoted to the study of QCD equation of state in external magnetic field and nonzero baryon density. Our study is carried out by means of lattice simulation with 2+1 dynamical staggered quarks at the physical masses. The simulation is conducted at imaginary baryon chemical potential what allowed us to overcome the sign problem. We expand the pressure in the baryon imaginary chemical potential and study three leading nonzero coefficients in this expansion. These coefficients were calculated for the following values of magnetic field: $eB=0.3$, $0.6$, $1.2$ GeV$^2$ with the lattice sizes $8\times32^3$, $10\times40^3$, $12\times48^3$. Using these data we take continuum limit for the coefficients. Our results indicate considerable enhancement of the expansion coefficients by the magnetic field.

hep-lat↗

arXiv2022

Thermal phase transitions in rotating QCD with dynamical quarks

Relativistic rotation causes a change of QCD critical temperatures. Various phenomenological and effective models predict a decrease of the critical temperatures in rotating QCD. Nevertheless, lattice simulations showed that the critical temperature in gluodynamics increases due to rotation. We extend the lattice study to the theory with dynamical fermions. We present the first lattice results for rotating QCD with $N_f=2$ dynamical clover-improved Wilson quarks. We also study separately the effect of rotation on gluonic and fermionic degrees of freedom. It is shown that separate rotations of gluons and fermions have opposite effects on the critical temperatures. In aggregate, the pseudo-critical temperatures in QCD increase with angular velocity. Dependence of the results on the pion mass is also discussed.

hep-lat↗

arXiv2022

Equation of State of dense QCD in external magnetic field

In this proceeding we present our first results of the study of the QCD Equation of State at non-zero baryon density and in external magnetic field. We focused on the first three non-vanishing expansion coefficients of pressure in chemical potential and their dependence on magnetic field. The study is carried out within lattice simulations with $N_f=2+1$ dynamical quarks with physical quark masses. To overcome the sign problem, the simulations are carried out at imaginary baryon chemical potential. Our results suggest that external magnetic field considerably enhances the expansion coefficients and modifies their dependence on temperature.

hep-lat↗

arXiv2022

Lattice study of the confinement/deconfinement transition in rotating gluodynamics

We study the influence of relativistic rotation on the confinement/deconfinement phase transition in gluodynamics by means of lattice simulations. The simulation is performed in the reference frame which rotates with the system under investigation, where rotation is reduced to external gravitational field. The Polyakov loop and its susceptibility are calculated for various lattice parameters and values of angular velocities which are characteristic for heavy-ion collision experiments. Different types of boundary conditions (open, periodic, Dirichlet) are imposed in directions, orthogonal to rotation axis. It is shown, that the critical temperature of the confinement/deconfinement transition in gluodynamics grows quadratically with increasing angular velocity. This conclusion does not depend on the boundary conditions used in our study and we believe that this is universal property of gluodynamics. We also present first results of the study of the phase diagram of rotating QCD matter with fermions. The results indicate, that effect of the rotation on fermions is opposite to gluons: it leads to the decrease of the critical temperature.

hep-lat↗

arXiv2021

Electromagnetic conductivity of quark-gluon plasma at non-zero baryon density

In this preprint we present our results on the study of the electromagnetic conductivity in dense quark-gluon plasma obtained within lattice simulations with $N_f = 2 + 1$ dynamical quarks. We employ stout improved rooted staggered quarks at the physical point and the tree-level Symanzik improved gauge action. The simulations are performed at imaginary baryon chemical potential, and the Tikhonov regularisation method is used to extract the conductivity from current-current correlators. Our results indicate an increase of QGP electromagnetic conductivity with real baryon density, and this dependence is quite strong.

hep-lat↗

arXiv2021

Influence of relativistic rotation on the confinement/deconfinement transition in gluodynamics

In this paper we consider the influence of relativistic rotation on the confinement/deconfinement transition in gluodynamics within lattice simulation. We perform the simulation in the reference frame which rotates with the system under investigation, where rotation is reduced to external gravitational field. To study the confinement/deconfinement transition the Polyakov loop and its susceptibility are calculated for various lattice parameters and the values of angular velocities which are characteristic for heavy-ion collision experiments. Different types of boundary conditions (open, periodic, Dirichlet) are imposed in directions, orthogonal to rotation axis. Our data for the critical temperature are well described by a simple quadratic function $T_c(Ω)/T_c(0) = 1 + C_2 Ω^2$ with $C_2>0$ for all boundary conditions and all lattice parameters used in the simulations. From this we conclude that the critical temperature of the confinement/deconfinement transition in gluodynamics increases with increasing angular velocity. This conclusion does not depend on the boundary conditions used in our study and we believe that this is universal property of gluodynamics.

hep-lat↗

arXiv2020

Lattice study of thermodynamic properties of dense QC$_2$D

In this paper we study thermodynamic properties of dense cold $SU(2)$ QCD within lattice simulation with dynamical rooted staggered quarks which in the continuum limit correspond to $N_f=2$ quark flavours. We calculate baryon density, renormalized chiral and diquark condensates for various baryon chemical potentials in the region $μ\in (0,\,2000)$ MeV. It is found, that in the region $μ\in (0,\,540)$ MeV the system is well described by the ChPT predictions. In the region $μ> 540$ MeV the system becomes sufficiently dense and ChPT is no longer applicable to describe lattice data. For chemical potentials $μ> 900$ MeV we observe formation of the Fermi sphere, and the system is similar to the one described by the Bardeen-Cooper-Schrieffer theory where the the diquarks play a role of Cooper pairs. In order to study how nonzero baryon density influences the gluon background we calculate chromoelectric and chromomagnetic fields, as well as the topological susceptibility. We find that the chromoelectric field and the topological susceptibility decrease, whereas the chromomagnetic field increases with rising of baryon chemical potential. Finally we study the equation of state of dense two-color quark matter.

hep-lat↗

arXiv2020

Effects of Dense Quark Matter on Gluon Propagators in Lattice QC$_2$D

The transverse and longitudinal gluon propagators in the Landau gauge are studied in the two-color lattice QCD at nonzero quark chemical potential $μ_q$. Parameterization of the momentum dependence of the propagators is provided for all values of chemical potential under study. We find that the longitudinal propagator is infrared suppressed at nonzero $μ_q$ with suppression increasing with increasing $μ_q$. The transverse propagator dependence on $μ_q$ was found to be opposite: it is enhanced at large $μ_q$. It is found, respectively, that the electric screening mass is increasing while the magnetic screening mass is decreasing with increasing $μ_q$. Nice agreement between the electric screening mass computed from the longitudinal propagator and the Debye mass computed earlier from the singlet static quark-antiquark potential was found. We discuss how the dependence of the propagators on the chemical potential correlates with the respective dependence of the string tension. Additionally, we consider the difference between two propagators as a function of the momentum and make interesting observations.

hep-lat↗

arXiv2019

Lattice study of QCD at finite chiral density: topology and confinement

In this paper we study the properties of QCD at nonzero chiral density $ρ_5$, which is introduced through chiral chemical potential $μ_5$. The study is performed within lattice simulation of QCD with dynamical rooted staggered fermions. We first check that $ρ_5$ is generated at nonzero $μ_5$ and in the chiral limit observe $ρ_5 \sim Λ_{QCD}^2 μ_5$. We also test the possible connection between confinement and topological fluctuations. To this end, we measured the topological susceptibility $χ_{\mbox{\footnotesize top}}$ and string tension $σ$ for various values of $μ_5$. We observed that both string tension and chiral susceptibility grow with $μ_5$ and there is a strong correlation between these quantities. We thus conclude that the chiral chemical potential enhances topological fluctuations and that these fluctuations can indeed be closely related to the strength of confinement.

hep-lat↗

arXiv2019

Finite-density QCD transition in magnetic field background

Using numerical simulations of lattice QCD with physical quark masses, we reveal the influence of magnetic-field background on chiral and deconfinement crossovers in finite-temperature QCD at low baryonic density. In the absence of thermodynamic singularity, we identify these transitions with inflection points of the approximate order parameters: normalized light-quark condensate and renormalized Polyakov loop, respectively. We show that the quadratic curvature of the chiral transition temperature in the ``temperature--chemical potential'' plane depends rather weakly on the strength of the background magnetic field. At weak magnetic fields, the thermal width of the chiral crossover gets narrower as the density of the baryon matter increases, possibly indicating a proximity to a real thermodynamic phase transition. Remarkably, the curvature of the chiral thermal width flips its sign at $eB_{\mathrm{fl}} \simeq 0.6\,\mathrm{GeV}^2$, so that above the flipping point $B > B_{\mathrm{fl}}$, the chiral width gets wider as the baryon density increases. Approximately at the same strength of magnetic field, the chiral and deconfining crossovers merge together at $T \approx 140\,\mathrm{MeV}$. The phase diagram in the parameter space ``temperature-chemical potential-magnetic field'' is outlined, and single-quark entropy and single-quark magnetization are explored. The curvature of the chiral thermal width allows us to estimate an approximate position of the chiral critical endpoint at zero magnetic field: $(T_c^{\text{CEP}}, μ_B^{\text{CEP}})= (100(25)\, \text{MeV},\ 800(140)\,\text{MeV})$.

hep-lat↗

arXiv2019

Catalysis of Dynamical Chiral Symmetry Breaking by Chiral Chemical Potential in Dirac semimetals

In this paper we study how dynamical chiral symmetry breaking is affected by nonzero chiral chemical potential in Dirac semimetals. To perform this study we applied lattice quantum Monte Carlo simulations of Dirac semimetals. Within lattice simulation we calculated the chiral condensate for various fermion masses, the chiral chemical potentials and effective coupling constants. For all parameters under consideration we have found that the chiral condensate is enhanced by chiral chemical potential. Thus our results confirms that in Dirac semimetals the chiral chemical potential plays a role of the catalyst of the dynamical chiral symmetry breaking.

cond-mat.str-el↗

arXiv2019

Lattice study of static quark-antiquark interactions in dense quark matter

In this paper we study the interactions among a static quark-antiquark pair in the presence of dense two-color quark matter with lattice simulation. To this end we compute Polyakov line correlation functions and determine the renormalized color averaged, color singlet and color triplet grand potentials. The color singlet grand potential allows us to elucidate the number of quarks induced by a static quark antiquark source, as well as the internal energy of such a pair in dense quark matter. We furthermore determine the screening length, which in the confinement phase is synonymous with the string breaking distance. The screening length is a decreasing function of baryon density, due to the possibility to break the interquark string via a scalar diquark condensate at high density. We also study the large distance properties of the color singlet grand potential in a dense medium and find that it is well described by a simple Debye screening formula, parameterized by a Debye mass and an effective coupling constant. The latter is of order of unity, i.e. even at large density two-color quark matter is a strongly correlated system.

hep-lat↗

arXiv2018

Temperature dependence of bulk viscosity within lattice simulation of $SU(3)$--gluodynamics

In this paper the temperature dependence of the $SU(3)$--gluodynamics bulk viscosity is studied within lattice simulations. To carry out this study we measure the correlation function of the trace of the energy-momentum tensor for a set of temperatures within the range $T/T_c \in (0.9, 1.5)$. To extract the bulk viscosity from the correlation function we apply the Backus-Gilbert method and the Tikhonov regularization method. We show that the ratio $ζ/s$ is small in the region $T/T_c \geqslant 1.1-1.2$ and in the vicinity of the transition $T/T_c \leqslant 1.1-1.2$ it quickly rises. Our results are in agreement with previous lattice studies and in a reasonable agreement with other phenomenological approaches. Obtained values of the bulk viscosity are significantly larger than perturbative results, what confirms that QGP is a strongly correlated system.

hep-lat↗

arXiv2017

Lattice Quantum Monte Carlo Study of Chiral Magnetic Effect in Dirac Semimetals

In this paper Chiral Magnetic Effect (CME) in Dirac semimetals is studied by means of lattice Monte Carlo simulation. We measure conductivity of Dirac semimetals as a function of external magnetic field in parallel $σ_{\parallel}$ and perpendicular $σ_{\perp}$ to the external field directions. The simulations are carried out in three regimes: semimetal phase, onset of the insulator phase and deep in the insulator phase. In the semimetal phase $σ_{\parallel}$ grows whereas $σ_{\perp}$ drops with magnetic field. Similar behaviour was observed in the onset of the insulator phase but conductivity is smaller and its dependence on magnetic field is weaker. Finally in the insulator phase conductivities $σ_{\parallel, \perp}$ are close to zero and do not depend on magnetic field. In other words, we observe manifestation of the CME current in the semimetal phase, weaker manifestation of the CME in the onset of the insulator phase. We do not observe signatures of CME in the insulator phase. We believe that the suppression of the CME current in the insulator phase is connected to chiral symmetry breaking and generation of dynamical fermion mass which take place in this phase.

cond-mat.str-el↗