arXiv subjects

D. N. Voskresensky

Publications and source records attributed to D. N. Voskresensky.

At least 55 records · Page 3Linked to original sources

arXiv2013

Nuclear medium cooling scenario in the light of new Cas A cooling data and the 2 M_sun pulsar mass measurements

Recently, Elshamounty et al. performed a reanalysis of the surface temperature of the neutron star in the supernova remnant Cassiopeia A on the basis of Chandra data measured during last decade, and added a new data point. We show that all reliably known temperature data of neutron stars including those belonging to Cassiopea A can be comfortably explained in our "nuclear medium cooling" scenario of neutron stars. The cooling rates account for medium-modified one-pion exchange in dense matter, polarization effects in the pair-breaking-formation processes operating on superfluid neutrons and protons paired in the 1S_0 state, and other relevant processes. The emissivity of the pair-breaking-formation process in the 3P_2 state is a tiny quantity within our scenario. Crucial for a successful description of the Cassiopeia A cooling proves to be the thermal conductivity from both, the electrons and nucleons, being reduced by medium effects. Moreover, we exploit an EoS which stiffens at high densities due to an excluded volume effect and is capable of describing a maximum mass of 2.1 M_sun, thus including the recent measurements of PSR J1614-2230 and PSR J0348+0432.

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arXiv2013

Remarks concerning bulk viscosity of hadron matter in relaxation time ansatz

The bulk viscosity is calculated for hadron matter produced in heavy-ion collisions, being described in the relaxation time approximation withi n the relativistic mean- field-based model with scaled hadron masses and couplings. W e show how different approximations used in the literature affect the result. Nume rical evaluations of the bulk viscosity with three considered models deviate not much from each other confirming earlier results.

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arXiv2013

Non-Equilibrium 2PI Potential and Its Possible Application to Evaluation of Bulk Viscosity

Within non-equilibrium Green's function technique on the real-time contour and the two-particle-irreducable (2PI) $Φ$-functional method, a non-equilibrium potential is introduced. It naturally generalizes the conventional thermodynamic potential with which it coincides in thermal equilibrium. Variations of the non-equilibrium potential over respective parameters result in the same quantities as those of the thermodynamic potential but in arbitrary non-equilibrium. In particular, for slightly non-equilibrium inhomogeneous configurations a variation of the non-equilibrium potential over volume is associated with the trace of the non-equilibrium stress tensor. The latter is related to the bulk viscosity. This provides a novel way for evaluation of the bulk viscosity.

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arXiv2013

Time delays and advances in classical and quantum systems

The paper reviews positive and negative time delays in various processes of classical and quantum physics. In the beginning, we demonstrate how a time-shifted response of a system to an external perturbation appears in classical mechanics and classical electrodynamics. Then we quantify durations of various quantum mechanical processes. The duration of the quantum tunneling is studied. An interpretation of the Hartman paradox is suggested. Time delays and advances appearing in the three-dimensional scattering problem on a central potential are considered. Then we discuss delays and advances appearing in quantum field theory and after that we focus on the issue of time delays and advancements in quantum kinetics. We discuss problems of the application of generalized kinetic equations in simulations of the system relaxation towards equilibrium and analyze the kinetic entropy flow. Possible measurements of time delays and advancements in experiments similar to the recent OPERA neutrino experiment are also discussed.

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arXiv2012

Screening and anti-screening in QED and in Weyl semimetals

Distributions of charge near charged impurities in Weyl semimetals are considered with the help of relativistic Thomas-Fermi method in full analogy with the solutions previously found in QED. Screening and anti-screening, zero charge and asymptotic freedom solutions appearing in different physical situations are discussed.

cond-mat.mes-hall↗

arXiv2012

Strangeness Balance in HADES Experiments and the Xi- Enhancement

HADES data on a strangeness production in Ar+KCl collisions at 1.76A GeV are analyzed within a minimal statistical model. The total negative strangeness content is fixed by the observed K^+ multiplicities on event-by-event basis. Particles with negative strangeness are assumed to remain in chemical equilibrium with themselves and in thermal equilibrium with the environment until a common freeze-out. Exact strangeness conservation in each collision event is explicitly preserved. This implies that Xi baryons can be released only in events where two or more kaons are produced. An increase of the fireball volume due to application of a centrality trigger in HADES experiments is taken into account. We find that experimental ratios of K-/K+, Lambda/K+ and Sigma/K+ can be satisfactorily described provided in-medium potentials are taken into account. However, the calculated Xi-/Lambda/K+ ratio proves to be significantly smaller compared to the measured value (8 times lower than the experimental median value and 3 times lower than the lower error bar). Various scenarios to explain observed Xi enhancement are discussed. Arguments are given in favor of the Xi production in direct reactions. The rates of the possible production processes are estimated and compared.

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arXiv2011

Relaxation time ansatz and shear and bulk viscosities of gluon matter

Shear and bulk viscosity-to-entropy density ratios are calculated for the pure gluon matter in a non-equilibrium mean-field quasiparticle approach within the relaxation time approximation. We study how different approximations used in the literature affect the results for the shear and bulk viscosities. Though the results for the shear viscosity turned out to be quite robust, all evaluations of the shear and bulk viscosities obtained in the framework of the relaxation time approximation can be considered only as rough estimations.

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arXiv2011

Spin excitonic and diffusive modes in superfluid Fermi liquids

A role of a particle-particle p-wave spin interaction in Fermi liquids with s-wave pairing is studied. Depending on the sign of the interaction there arises either the new exciton collective mode below the pair-breaking threshold or the diffusive excitation mode above the threshold. The Landau parameters which control the interaction strength are evaluated for various systems: the dilute fermion gases, degenerate electron liquid, metals, atomic nuclei and neutron matter. The interaction removes also the square-root singularity in the phase space of pair breaking processes. It is shown how these effects influence the neutrino emissivity in the neutron Cooper-pair recombinations in neutron stars.

cond-mat.supr-con↗

arXiv2011

On the Cooling of the Neutron Star in Cassiopeia A

We demonstrate that the high-quality cooling data observed for the young neutron star in the supernova remnant Cassiopeia A over the past 10 years--as well as all other reliably known temperature data of neutron stars--can be comfortably explained within the "nuclear medium cooling" scenario. The cooling rates of this scenario account for medium-modified one-pion exchange in dense matter and polarization effects in the pair-breaking formations of superfluid neutrons and protons. Crucial for the successful description of the observed data is a substantial reduction of the thermal conductivity, resulting from a suppression of both the electron and nucleon contributions to it by medium effects. We also find that possibly in as little as about ten years of continued observation, the data may tell whether or not fast cooling processes are active in this neutron star.

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arXiv2011

Shear and bulk viscosities for pure glue matter

Shear $η$ and bulk $ζ$ viscosities are calculated in a quasiparticle model within a relaxation time approximation for pure gluon matter. Below $T_c$ the confined sector is described within a quasiparticle glueball model. Particular attention is paid to behavior of the shear and bulk viscosities near $T_c$. The constructed equation of state reproduces the first-order phase transition for the glue matter. It is shown that with this equation of state it is possible to describe the temperature dependence of the shear viscosity to entropy ratio $η/s$ and the bulk viscosity to entropy ratio $ζ/s$ in reasonable agreement with available lattice data but absolute values of the $ζ/s$ ratio underestimate the upper limits of this ratio in the lattice measurements typically by an order of magnitude.

nucl-th↗

arXiv2010

Viscosity and thermal conductivity effects at first-order phase transitions in heavy-ion collisions

Effects of viscosity and thermal conductivity on the dynamics of first-order phase transitions are studied. The nuclear gas-liquid and hadron-quark transitions in heavy-ion collisions are considered. We demonstrate that at non-zero thermal conductivity, $κ\neq 0$, onset of spinodal instabilities occurs on an isothermal spinodal line, whereas for $κ=0$ instabilities take place at lower temperatures, on an adiabatic spinodal.

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arXiv2010

Superfluid nucleon matter in and out of equilibrium and weak interactions

The Larkin-Migdal approach to a cold superfluid Fermi liquid is generalized for a non-equilibrium system. The Schwinger-Keldysh diagram technique is applied. The developed formalism is applicable to the pairing in the states with arbitrary angular momenta. We consider the white body radiation problem by calculating probabilities of different direct reactions from a piece of a fermion superfluid. The closed diagram technique is formulated in terms of the full Green's functions for systems with the pairing correlation. The cutting rules are used to classify the diagrams representing one-nucleon, two-nucleon, etc. processes in the matter. The important role of multi-piece diagrams for the vector-current conservation is demonstrated. In the case of equilibrated systems, dealing with dressed Green's functions, we demonstrate correspondence between calculations in the Schwinger-Kadanoff-Baym-Keldysh formalism and the ordinary Matsubara technique. As an example we consider neutrino radiation from the neutron pair breaking and formation processes in case of a singlet pairing. Necessary correlation effects are included. The in-medium renormalization of normal and anomalous vertices is performed.

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arXiv2010

Viscosity coefficients for hadron and quark-gluon phases

The shear ($η$) and bulk ($ζ$) viscosities are calculated in a quasiparticle relaxation time approximation. The hadron phase is described within the relativistic mean field based model with scaled hadron masses and couplings. The quark phase is treated in terms of the heavy quark bag model fitted to the lattice data. A two-phase model allowing for the first order phase transition from the hadron phase to the strongly coupled quark gluon plasma is constructed by means of the Gibbs conditions. Temperature and baryon density dependence of the calculated viscosity-to-entropy ratios ($η/s$, $ζ/s$) are analyzed and compared with those obtained in other models. Special attention is paid to the behavior of viscosity coefficients near the critical temperature, from both hadron and quark-gluon side. Effects of resonance widths on viscosities and viscosity-to-entropy ratios are estimated.

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arXiv2010

Hydrodynamics of Resonances

We derive system of equations describing fluidity of the medium consisting of non-relativistic particles with finite mass-widths. For that we use expressions for the kinetic Noether 4-current and the Noether energy-momentum tensor being conserved provided one uses self-consistent approximations to the gradient expanded Kadanoff-Baym equations. Kinetic coefficients entering equations of non-ideal hydrodynamics of resonances are obtained in terms of the real and imaginary parts of the self-energies within a relaxation time approximation.

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arXiv2010

Thermal conductivity in dynamics of first-order phase transition

Effects of thermal conductivity on the dynamics of first-order phase transitions are studied. Important consequences of a difference of the isothermal and adiabatic spinodal regions are discussed. We demonstrate that in hydrodynamical calculations at non-zero thermal conductivity, $κ\neq 0$, onset of the spinodal instability occurs, when the system trajectory crosses the isothermal spinodal line. Only for $κ= 0$ it occurs at a cross of the adiabatic spinodal line. Therefore ideal hydrodynamics is not suited for an appropriate description of first-order phase transitions.

nucl-th↗

arXiv2010

Neutral weak currents in nucleon superfluid Fermi liquids: Larkin-Migdal and Leggett approaches

Neutrino emission in processes of breaking and formation of nucleon Cooper pairs is calculated in the framework of the Larkin-Migdal and the Leggett approaches to the description of superfluid Fermi liquids at finite temperatures. We explain peculiarities of both approaches and explicitly demonstrate that they lead to the same expression for the emissivity in pair breaking and formation processes.

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arXiv2009

Viscosity of hadron matter within relativistic mean-field based model with scaled hadron masses and couplings

The shear ($η$) and bulk ($ζ$) viscosities are calculated in a quasiparticle relaxation time approximation for a hadron matter described within the relativistic mean-field based model with scaled hadron masses and couplings. Comparison with results of other models is presented. We demonstrate that a small value of the shear viscosity to entropy density ratio required for explaining a large elliptic flow observed at RHIC may be reached in the hadron phase. Large values of the bulk viscosity are noted in case of the baryon enriched matter.

nucl-th↗

arXiv2009

Hydrodynamical description of first-order phase transitions: Analytical treatment and numerical modeling

Solutions of hydrodynamical equations are presented for an equation of state allowing for a first-order phase transition. The numerical analysis is supplemented by analytical treatment provided the system is close to the critical point. The processes of growth and dissolution of seeds of various sizes and shapes in meta-stable phases (like super-cooled vapor and super-heated liquid) are studied, as well as the dynamics of unstable modes in the spinodal region. We show that initially nonspherical seeds acquire spherical shape with passage of time. Applications to the description of the first-order phase transitions in nuclear systems, such as the nuclear gas-liquid transition occurring in low energy heavy-ion collisions and the hadron-quark transition in the high energy heavy-ion collisions are discussed. In both cases we point out the important role played by effects of viscosity and surface tension. It is shown that fluctuations dissolve and grow as if the fluid were effectively very viscous. Even in the spinodal region seeds may grow slowly due to viscosity and critical slowing down. This prevents the enhancement of fluctuations in the near-critical region, which is frequently considered as a signal of the critical point in heavy-ion collisions.

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