arXiv subjects

V. I. Zakharov

Publications and source records attributed to V. I. Zakharov.

At least 19 recordsLinked to original sources

arXiv2025

Modeling of acceleration in heavy-ion collisions: occurrence of temperature below the Unruh temperature

It has recently been shown that extremely strong electric fields can be created in central collisions of heavy ions, due to which the Schwinger effect can be significant. A direct analogue of the electric field in hydrodynamics is the acceleration of the medium. Using the parton-hadron-string dynamics (PHSD) framework we model the Au-Au collisions at intermediate collision energies $\sqrt{s_{NN}}=4.5-11.5\,$GeV and obtain the spatial distribution of acceleration at different time moments. The present study demonstrates that extremely high acceleration of the order of 1 GeV may be generated in both central and non-central collisions, and that the distribution exhibits a core-corona structure. Consequently, in contrast to the case with an electric field, the Unruh effect is expected to be significant. It is demonstrated that for the confined phase the temperature is less than the Unruh temperature. Conversely, in the deconfined phase, the relationship is inverse. The obtained results thus support the prediction about the existence of states with $T<T_U$ at the early stages of the collision and the associated complementary description of thermalization in terms of the novel phase transition at the Unruh temperature.

nucl-th↗

arXiv2024

Hydrodynamical duals of the gravitational axial anomaly and the cosmological constant

We construct the hydrodynamic expansion for a rotating and accelerated medium in a curved space-time, and establish a duality between the currents related to the cosmological constant and the acceleration. Then we consider the more general case with a non-zero Weyl tensor, and show the relationship between the current in flat space-time and the gravitational axial anomaly. This generalizes the previous derivation to the case with a non-zero Ricci tensor.

hep-th↗

arXiv2023

Unruh effect in curved space-time and hydrodynamics

We consider an accelerated relativistic fluid in four-dimensional (anti-)de Sitter space-time. Analyzing only hydrodynamic equations, we construct the equilibrium stress-energy tensor. We confirm that (A)dS vacuum corresponds to a thermal bath in the accelerated frame with a temperature, depending on the acceleration in a flat higher-dimensional (namely, five-dimensional) space, in which curved space-times are embedded. We develop the duality between hydrodynamics and gravity finding a direct relationship between the transport coefficients in flat and curved space-times.

hep-th↗

arXiv2023

Chiral effects: new trends

By chiral effects one understands manifestations of chiral gauge anomaly and of gravitational chiral anomaly in hydrodynamics. In recent two-three years our understanding of the chiral effects has considerably changed. Here we present mini-review of two topics. First, shift in understanding symmetry which underlies the chiral magnetic effect and, second, interpretation of the chiral kinematical effect uncovered recently.

hep-th↗

arXiv2022

Hydrodynamic manifestations of gravitational chiral anomaly

The conservation of an axial current modified by the gravitational chiral anomaly implies the universal transport phenomenon (Kinematical Vortical Effect) dependent solely on medium vorticity and acceleration but not dependent explicitly on its temperature and density. This general analysis is verified for the case of massless fermions with spin 1/2.

hep-th↗

arXiv2022

Gravitational chiral anomaly for spin 3/2 field interacting with spin 1/2 field

The gravitational chiral quantum anomaly is calculated in the framework of the extended Rarita-Schwinger-Adler (RSA) field theory, which includes the interaction with an additional spin 1/2 field. It is shown that the factor in the gravitational chiral anomaly, normalized to the Dirac field anomaly, is equal to -19. The resulting value distinguishes the RSA theory from the other theories of spin 3/2. A direct verification of the conformality of the RSA theory in the strong interaction limit at the level of one-loop three-point graphs was made.

hep-th↗

arXiv2021

Chiral Vortical Effect in Extended Rarita-Schwinger Field Theory and Chiral Anomaly

We consider the theory of Rarita-Schwinger field interacting with a field with spin 1/2, in the case of finite temperature, chemical potential and vorticity, and calculate the chiral vortical effect for spin 3/2. We have clearly demonstrated the role of interaction with the spin 1/2 field, the contribution of the terms with which to CVE is 6. Since the contribution from the Rarita-Schwinger field is -1, the overall coefficient in CVE is 6-1=5, which corresponds to the recent prediction of a gauge chiral anomaly for spin 3/2. The obtained values for the coefficients $μ^2$ and $T^2$ are proportional to each other, but not proportional to the spin, which indicates a possible new universality between the temperature-related and the chemical potential-related vortical effects. The results obtained allow us to speculate about the relationship between the gauge and gravitational chiral anomalies.

hep-th↗

arXiv2021

On chiral vortical effect in accelerated matter

We revisit the evaluation of the chiral vortical effect in the accelerated matter. To first order in the acceleration the corresponding matrix element of the axial current can be reconstructed from the flat-space limit. A crucial point is the existence in the this case of an extra conservation law of fluid helicity. As a result, the chirality of the microscopic degrees of freedom and helicity of the macroscopic motion are separately conserved. This separation persists also in presence of gravity. Implications for the thermal chiral vortical effect are discussed.

hep-th↗

arXiv2020

CVE for photons: black-hole vs. flat-space derivation

The chiral vortical effect (CVE) was derived first for non-interacting massless fermions. Recently, an alternative derivation of the CVE was suggested which relates it to the radiation from the horizon of a rotating black hole. We attempt to generalize the latter derivation to the case of photons and encounter a crucial factor of two difference between the two ways of visualizing the CVE. Reservations and possible explanations are briefly discussed.

hep-th↗

arXiv2020

Chiral vortical effect for vector fields

We consider photonic vortical effect, i.e. the difference of the flows of left- and right-handed photons along the vector of angular velocity in rotating photonic medium. Two alternative frameworks to evaluate the effect are considered, both of which have already been tried in the literature. First, the standard thermal fied theory and, alternatively, Hawking-radiation-type derivation. In our earlier attempt to compare the two approaches, we found a crucial factor of two difference. Here we revisit the problem, paying more attention to details of infrared regularizations. We find out that introduction of an infinitesimal mass of the vector field brings the two ways of evaluating the chiral vortical effect into agreement with each other. Some implications, both on the theoretical and phenomenological sides, are mentioned.

hep-th↗

arXiv2018

Lattice QCD thermodynamics at finite chemical potential and its comparison with Experiments

We compare higher moments of baryon numbers measured at the RHIC heavy ion collision experiments with those by the lattice QCD calculations. We employ the canonical approach, in which we can access the real chemical potential regions avoiding the sign problem. In the lattice QCD simulations, we study several fits of the number density in the pure imaginary chemical potential, and analyze how these fits affects behaviors at the real chemical potential. In the energy regions between $\sqrt{s}_{NN}$=19.6 and 200 GeV, the susceptibility calculated at $T/T_c=0.93$ is consistent with experimental data at $0 \le μ_B/T < 1.5$, while the kurtosis shows similar behavior with that of the experimental data in the small $μ_B/T$ regions $0 \le μ_B/T < 0.3$. The experimental data at $\sqrt{s}_{NN}=$ 11.5 shows quite different behavior. The lattice result in the deconfinement region,$T/T_c=1.35$, is far from experimental data.

hep-lat↗

arXiv2018

Lee-Yang zeros in lattice QCD for searching phase transition points

We report Lee-Yang zeros behavior at finite temperature and density. The quark number densities, , are calculated at the pure imaginary chemical potential, where no sign problem occurs. Then, the canonical partition functions, Z_C(n,T,V), up to some maximal values of n are estimated through fitting theoretically motivated functions to , which are used to compute the Lee-Yang zeros. We study the temperature dependence of the distributions of the Lee-Yang zeros around the pseudo-critical temperature region T/T_c = 0.84 - 1.35. In the distributions of the Lee-Yang zeros, we observe the Roberge-Weiss phase transition at T/T_c >= 1.20. We discuss the dependence of the behaviors of Lee-Yang zeros on the maximal value of n, so that we can estimate a reliable infinite volume limit.

hep-lat↗

arXiv2018

IR properties of chiral effects in pionic matter

Chiral effects exhibit peculiar universality in idealized theoretical limits. However, they are known to be infrared sensitive and get modified in more realistic settings. In this work, we study how the corresponding conductivities vary with the constituent mass. We concentrate on a pionic realization of chiral effects which provides a better control over infrared properties of the theory. The pionic medium is considered at finite vector and axial isospin chemical potentials in the presence of an external magnetic field. This system supports electric and axial isospin currents along the magnetic field which correspond to chiral magnetic and chiral separation effects. We show that these currents are sensitive to the finite mass of the constituents, but the conductivities follow a simple scaling with the corresponding charge densities as one would expect for polarization effects. It is argued that this relation can capture the dependence of chiral effects on other infrared parameters. Finally, we briefly comment on the realization of the 't Hooft matching condition in pionic media at finite densities.

hep-ph↗

arXiv2018

Chiral fluids: a few theoretical issues

We review briefly a few topics concerning physics of fluids whose constituents are massless fermions interacting in chiral invariant way. Macroscopic manifestations of the chral anomaly is one of central issues. Another topic is ultraviolet vs infrared sensistivity of chiral magnetic and vortical effects. To clarify dynamical issues involved we rely mostly on a (well-known) toy model of pionic superfluidity.

hep-th↗

arXiv2018

Quark-hadron duality in hydrodynamics: an example

We consider the problem of transferring overall rotation of quark-gluon plasma to polarization of hyperons along the rotation axis. As a toy theoretical model, we exploit that of pionic superfluidity induced by chemical potentials violating isotopic symmetry. Apparently, the model accounts only for the light degrees of freedom, that is pions. The rotation, however, results in vortices which are infinitely thin in the hydrodynamic approximation. Field theory resolves the singularity and predicts that the core of the vortices is build up on spins of baryons. We review consequences from the quark-hadron duality in this case. First, an anomalous triangle graph in effective field theory turns to be dual to the vorticity term in the standard hydrodynamic expansion. And, then, the overall coefficient determining the polarization of baryons is fixed by duality with the triangle graph in the fundamental field theory.

hep-th↗

arXiv2017

Lattice QCD at finite baryon density using analytic continuation

We simulate lattice QCD with two flavors of Wilson fermions at imaginary baryon chemical potential. Results for the baryon number density computed in the confining and deconfining phases at imaginary baryon chemical potential are used to determine the baryon number density and higher cumulants at the real chemical potential via analytical continuation.

hep-lat↗

arXiv2017

Restoring canonical partition functions from imaginary chemical potential

Using GPGPU techniques and multi-precision calculation we developed the code to study QCD phase transition line in the canonical approach. The canonical approach is a powerful tool to investigate sign problem in Lattice QCD. The central part of the canonical approach is the fugacity expansion of the grand canonical partition functions. Canonical partition functions $Z_n(T)$ are coefficients of this expansion. Using various methods we study properties of $Z_n(T)$. At the last step we perform cubic spline for temperature dependence of $Z_n(T)$ at fixed $n$ and compute baryon number susceptibility $χ_B/T^2$ as function of temperature. After that we compute numerically $\partialχ/ \partial T$ and restore crossover line in QCD phase diagram. We use improved Wilson fermions and Iwasaki gauge action on the $16^3 \times 4$ lattice with $m_π/m_ρ = 0.8$ as a sandbox to check the canonical approach. In this framework we obtain coefficient in parametrization of crossover line $T_c(μ_B^2)=T_c\left(c-κ\, μ_B^2/T_c^2\right)$ with $κ= -0.0453 \pm 0.0099$.

hep-lat↗

arXiv2016

Study of lattice QCD at finite chemical potential using canonical ensemble approach

New approach to computation of canonical partition functions in $N_f=2$ lattice QCD is presented. We compare results obtained by new method with results obtained by known method of hopping parameter expansion. We observe agreement between two methods indicating validity of the new method. We use results for the number density obtained in the confining and deconfining phases at imaginary chemical potential to determine the phase transition line at real chemical potential.

hep-lat↗