41 research outputs found
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.Comment: 24 pages, 3 figure
Shear and bulk viscosities for pure glue matter
Shear and bulk viscosities are calculated in a quasiparticle
model within a relaxation time approximation for pure gluon matter. Below
the confined sector is described within a quasiparticle glueball model.
Particular attention is paid to behavior of the shear and bulk viscosities near
. 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 and the bulk viscosity to entropy ratio in
reasonable agreement with available lattice data but absolute values of the
ratio underestimate the upper limits of this ratio in the lattice
measurements typically by an order of magnitude.Comment: 8 pages, 4 figures; the published versio
Electromagnetic field evolution in relativistic heavy-ion collisions
The hadron string dynamics (HSD) model is generalized to include the creation
and evolution of retarded electromagnetic fields as well as the influence of
the magnetic and electric fields on the quasiparticle propagation. The
time-space structure of the fields is analyzed in detail for non-central Au+Au
collisions at 200 GeV. It is shown that the created magnetic
field is highly inhomogeneous but in the central region of the overlapping
nuclei it changes relatively weakly in the transverse direction. For the impact
parameter 10 fm the maximal magnetic field - perpendicularly to the
reaction plane - is obtained of order 5 for a very short time
0.2 fm/c, which roughly corresponds to the time of a maximal overlap of
the colliding nuclei. We find that at any time the location of the maximum in
the distribution correlates with that of the energy density of the
created particles. In contrast, the electric field distribution, being also
highly inhomogeneous, has a minimum in the center of the overlap region.
Furthermore, the field characteristics are presented as a function of the
collision energy and the centrality of the collisions. To explore the effect of
the back reaction of the fields on hadronic observables a comparison of HSD
results with and without fields is exemplified. Our actual calculations show no
noticeable influence of the electromagnetic fields - created in heavy-ion
collisions - on the effect of the electric charge separation with respect to
the reaction plane.Comment: 17 pages, 22 figures, title changed by editor, accepted for PR
Neutrino emission due to Cooper-pair recombination in neutron stars revisited
Neutrino emission in processes of breaking and formation of neutron and
proton Cooper pairs is calculated within the Larkin-Migdal-Leggett approach for
a superfluid Fermi liquid. We demonstrate explicitly that the Fermi-liquid
renormalization respects the Ward identity and assures the weak vector current
conservation. The systematic expansion of the emissivities for small
temperatures and nucleon Fermi velocity, v_{F,i}, i=n,p, is performed. Both
neutron and proton processes are mainly controlled by the axial-vector current
contributions, which are not strongly changed in the superfluid matter. Thus,
compared to earlier calculations the total emissivity of processes on neutrons
paired in the 1S_0 state is suppressed by a factor ~(0.9-1.2) v_{F,n}^2. A
similar suppression factor (~v_{F,p}^2) arises for processes on protons.Comment: 12 pages, 1 figur
Contribution of the massive photon decay channel to neutrino cooling of neutron stars
We consider massive photon decay reactions via intermediate states of
electron-electron-holes and proton-proton-holes into neutrino-antineutrino
pairs in the course of neutron star cooling. These reactions may become
operative in hot neutron stars in the region of proton pairing where the photon
due to the Higgs-Meissner effect acquires an effective mass that
is small compared to the corresponding plasma frequency. The contribution of
these reactions to neutrino emissivity is calculated; it varies with the
temperature and the photon mass as
for . Estimates show that these processes appear as extra
efficient cooling channels of neutron stars at temperatures K.Comment: accepted to publication in Zh. Eksp. Teor. Fiz. (JETP
Quark deconfinement and implications for the radius and the limiting mass of compact stars
We study the consequences of the hadron-quark deconfinement phase transition
in stellar compact objects when finite size effects between the deconfined
quark phase and the hadronic phase are taken into account. We show that above a
threshold value of the central pressure (gravitational mass) a neutron star is
metastable to the decay (conversion) to a hybrid neutron star or to a strange
star. The "mean-life time" of the metastable configuration dramatically depends
on the value of the stellar central pressure. We explore the consequences of
the metastability of ``massive'' neutron stars and of the existence of stable
compact quark stars (hybrid neutron stars or strange stars) on the concept of
limiting mass of compact stars. We discuss the implications of our scenario on
the interpretation of the stellar mass and radius extracted from the spectra of
several X-ray compact sources. Finally, we show that our scenario implies, as a
natural consequence a two step-process which is able to explain the inferred
``delayed'' connection between supernova explosions and GRBs, giving also the
correct energy to power GRBs.Comment: 34 pages, 10 figure
Lattice QCD Constraints on Hybrid and Quark Stars
A QCD-motivated dynamical-quasiparticle model with parameters adjusted to
reproduce the lattice-QCD equation of state is extrapolated from region of high
temperatures and moderate baryonic densities to the domain of high baryonic
densities and zero temperature. The resulting equation of state matched with
realistic hadronic equations of state predicts a phase transition into the
quark phase at higher densities than those reachable in neutron star interiors.
This excludes the possibility of the existence of hybrid (hadron-quark) stars.
Pure quark stars are possible and have low masses, small radii and very high
central densities. Similar results are obtained for a simple bag model with
massive quarks, fitted to reproduce the same lattice results. Self-bound quark
matter is also excluded within these models. Uncertainties in the present
extrapolation re discussed. Comparison with standard bag models is made.Comment: 13 p., 8 figs., 7 tables, Version accepted by Phys. Rev.
Strange Exotic States and Compact Stars
We discuss the possible appearance of strange exotic multi-quark states in
the interior of neutron stars and signals for the existence of strange quark
matter in the core of compact stars. We show how the in-medium properties of
possible pentaquark states are constrained by pulsar mass measurements. The
possibility of generating the observed large pulsar kick velocities by
asymmetric emission of neutrinos from strange quark matter in magnetic fields
is outlined.Comment: 10 pages, invited talk given at the International Conference on
Strangeness in Quark Matter 2006 (SQM2006), UCLA, USA, March 26-31, 2006,
Journal of Physics G in press, refs. adde
Superfluid Response and the Neutrino Emissivity of Neutron Matter
{We calculate the neutrino emissivity of superfluid neutron matter in the
inner crust of neutron stars. We find that neutrino emission due to
fluctuations resulting from the formation of Cooper pairs at finite temperature
is highly suppressed in non-relativistic systems. This suppression of the pair
breaking emissivity in a simplified model of neutron matter with interactions
that conserve spin is of the order of for density fluctuations and
for spin fluctuations, where is the Fermi velocity of neutrons.
The larger suppression of density fluctuations arises because the dipole moment
of the density distribution of a single component system does not vary in time.
For this reason, we find that the axial current response (spin fluctuations)
dominates. In more realistic models of neutron matter which include tensor
interactions where the neutron spin is not conserved, neutrino radiation from
bremsstrahlung reactions occurs at order . Consequently, even with the
suppression factors due to superfluidity, this rate dominates near .
Present calculations of the pair-breaking emissivity are incomplete because
they neglect the tensor component of the nucleon-nucleon interaction
Gapless phases of color-superconducting matter
We discuss gapless color superconductivity for neutral quark matter in beta
equilibrium at zero as well as at nonzero temperature. Basic properties of
gapless superconductors are reviewed. The current progress and the remaining
problems in the understanding of the phase diagram of strange quark matter are
discussed.Comment: 8 pages, 2 figures. Plenary talk at Strangeness in Quark Matter 2004
(SQM2004), Cape Town, South Africa, 15-20 September 2004. Minor correction