161 research outputs found
RMF models with -scaled hadron masses and couplings for description of heavy-ion collisions below 2A GeV
Within the relativistic mean-field framework with hadron masses and coupling
constants dependent on the mean scalar field we study properties of nuclear
matter at finite temperatures, baryon densities and isospin asymmetries
relevant for heavy-ion collisions at laboratory energies below 2 GeV.
Previously constructed (KVORcut-based and MKVOR-based) models for the
description of the cold hadron matter, which differ mainly by the density
dependence of the nucleon effective mass and symmetry energy, are extended for
finite temperatures. The baryon equation of state, which includes nucleons and
resonances is supplemented by the contribution of the pion gas
described either by the vacuum dispersion relation or with taking into account
the -wave pion-baryon interaction. Distribution of the charge between
components is found. Thermodynamical characteristics on plane are
considered. The energy-density and entropy-density isotherms are constructed
and a dynamical trajectory of the hadron system formed in heavy-ion collisions
is described. The effects of taking into account the isobars and the
-wave pion-nucleon interaction on pion differential cross sections, pion to
proton and ratios are studied. The liquid-gas first-order phase
transition is studied within the same models in isospin-symmetric and
asymmetric systems. We demonstrate that our models yield thermodynamic
characteristics of the phase transition compatible with available experimental
results. In addition, we discuss the scaled variance of baryon and electric
charge in the phase transition region. Effect of the non-zero surface tension
on spatial redistribution of the electric charge is considered for a possible
application to heavy-ion collisions at low energies.Comment: 26 pages, 17 figures; matches the submitted versio
Medium effects in the pion pole mechanism (photon photon --> pion-zero --> neutrino-R antineutrino-L (neutrino-L antineutrino-R)) of neutron star cooling
Nuclear medium effects in the neutrino cooling of neutron stars through the
exotic reaction channel \gamma \gamma --> \pi^0--> \nu_R \bar{\nu_L} (\nu_L
\bar{\nu_R}) are incorporated. Throughout the paper we discuss different
possibilities of right-handed neutrinos, massive left-handed neutrinos and
standard massless left-handed neutrinos (reaction is then allowed only with
medium modified vertices). It is demonstrated that multi-particle effects
suppress the rate of this reaction channel by 6-7 orders of magnitude that does
not allow to decrease existing experimental upper limit on the corresponding
\pi^0\nu\bar{\nu} coupling. Other possibilities of the manifestation of the
given reaction channel in differente physical situations, e.g. in the quark
color superconducting cores of some neutron stars, are also discussed. We
demonstrate that in the color-flavor-locked superconducting phase for
temperatures T < (0.1-10) MeV (depending on the effective pion mass and the
decay width) the process is feasibly the most efficient neutrino cooling
process, although the absolute value of the reaction is rather small.Comment: Replaced with revised version. New appendix, many clarifying
comments, corrected figs 3 and
Diquark Condensates and Compact Star Cooling
The effect of color superconductivity on the cooling of quark stars and
neutron stars with large quark cores is investigated. Various known and new
quark-neutrino processes are studied. As a result, stars being in the color
flavor locked (CFL) color superconducting phase cool down extremely fast. Quark
stars with no crust cool down too rapidly in disagreement with X-ray data. The
cooling of stars being in the N_f =2 color superconducting (2SC) phase with a
crust is compatible with existing X-ray data. Also the cooling history of stars
with hypothetic pion condensate nuclei and a crust does not contradict the
data.Comment: 10 pages, 5 figures, accepted for publication in Ap
BCS approximation to the effective vector vertex of superfluid fermions
We examine the effective interaction of nonrelativistic fermions with an
external vector field in superfluid systems. In contrast to the complicated
vertex equation, usually used in this case, we apply the approach which does
not employ an explicit form of the pairing interaction. This allows to obtain a
simple analytic expression for the vertex function only in terms of the order
parameter and other macroscopic parameters of the system. We use this effective
vertex to analyze the linear response function of the superfluid medium at
finite temperatures. At the time-like momentum transfer, the imaginary part of
the response function is found to be proportional to the fourth power of small
Fermi velocity, i.e. the energy losses through vector currents are strongly
suppressed. As an application, we calculate the neutrino energy losses through
neutral weak currents caused by the pair recombination in the superfluid
neutron matter at temperatures lower than the critical one for S-wave pairing.
This approach confirms a strong suppression of the neutrino energy losses as
predicted in Ref.[4].Comment: 19 pages, no figure
Viscosity coefficients for hadron and quark-gluon phases
The shear () and bulk () 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 (,
) 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.Comment: 56 pages, 22 figure
Relativistic Mean-Field Model with Scaled Hadron Masses and Couplings
Here we continue to elaborate properties of the relativistic mean-field based
model (SHMC) proposed in ref. [6] where hadron masses and coupling constants
depend on the -meson field. The validity of approximations used in [6]
is discussed. We additionally incorporate contribution of meson excitations to
the equations of motion. We also estimate the effects of the particle width. It
is demonstrated that the inclusion of the baryon-baryon hole and
baryon-antibaryon loop terms, if performed perturbatively, destroys the
consistency of the model.Comment: 44 pages, 14 figures; corrected according to referee's remarks,
version accepted for publication in Nucl. Phys.
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