348 research outputs found
Neutrino processes in the condensed phase of color flavor locked quark matter
We study weak interactions involving Goldstone bosons in the neutral kaon
condensed phase of color flavor locked quark matter. We calculate the rates for
the dominant processes that contribute to the neutrino mean free p ath and to
neutrino production. A light state, with a mass , where and are the quark
chemical potential and superconducting gap respectively, is shown to play an
important role. We identify unique characteristics of weak interaction rates in
this novel phase and discuss how they might influence neutrino emission in core
collapse supernova and neutron stars.Comment: 21 pages, 4 figure
Charge Neutrality of the Color-Flavor Locked Phase from the Low Energy Effective Theory
We investigate the issue of charge neutrality of the CFL phase of dense
quark matter using the low energy effective theory of high density QCD. We show
that the local electric and color charge neutrality of the ground state in a
homogeneous color superconducting medium follows from its dynamics. We also
consider the situation of a spatially inhomogeneous medium, such as may be
found in a neutron star core. We find that spatial inhomogeneity results in the
generation of electric fields, and positrons/electrons may be present in the
ground state. We estimate the concentration of charged leptons in the ground
state to be and consider their influence on the
opacity of the medium with respect to the modified photons.Comment: typos corrected, this version to appear in PR
Spin-one color superconductivity in compact stars?- an analysis within NJL-type models
We present results of a microscopic calculation using NJL-type model of
possible spin-one pairings in two flavor quark matter for applications in
compact star phenomenology. We focus on the color-spin locking phase (CSL) in
which all quarks pair in a symmetric way, in which color and spin states are
locked. The CSL condensate is particularly interesting for compact star
applications since it is flavor symmetric and could easily satisfy charge
neutrality. Moreover, the fact that in this phase all quarks are gapped might
help to suppress the direct Urca process, consistent with cooling models. The
order of magnitude of these small gaps (~1 MeV) will not influence the EoS, but
their also small critical temperatures (T_c ~800 keV) could be relevant in the
late stages neutron star evolution, when the temperature falls below this value
and a CSL quark core could form.Comment: 7 pages, 7 figures, revised version, accepted for the Conference
Proceedings of "Isolated Neutron Stars: from the Interior to the Surface",
London, 24-28. April 200
Numerical Portrait of a Relativistic BCS Gapped Superfluid
We present results of numerical simulations of the 3+1 dimensional Nambu -
Jona-Lasinio (NJL) model with a non-zero baryon density enforced via the
introduction of a chemical potential mu not equal to 0. The triviality of the
model with a number of dimensions d>=4 is dealt with by fitting low energy
constants, calculated analytically in the large number of colors (Hartree)
limit, to phenomenological values. Non-perturbative measurements of local order
parameters for superfluidity and their related susceptibilities show that, in
contrast to the 2+1 dimensional model, the ground-state at high chemical
potential and low temperature is that of a traditional BCS superfluid. This
conclusion is supported by the direct observation of a gap in the dispersion
relation for 0.5<=(mu a)<=0.85, which at (mu a)=0.8 is found to be roughly 15%
the size of the vacuum fermion mass. We also present results of an initial
investigation of the stability of the BCS phase against thermal fluctuations.
Finally, we discuss the effect of splitting the Fermi surfaces of the pairing
partners by the introduction of a non-zero isospin chemical potential.Comment: 41 pages, 19 figures, uses axodraw.sty, v2: minor typographical
correction
Effects of color superconductivity on the structure and formation of compact stars
We show that if color superconducting quark matter forms in hybrid or quark
stars it is possible to satisfy most of recent observational boundaries on
masses and radii of compact stellar objects. An energy of the order of
erg is released in the conversion from a (metastable) hadronic star
into a (stable) hybrid or quark star in presence of a color superconducting
phase. If the conversion occurs immediately after the deleptonization of the
proto-neutron star, the released energy can help Supernovae to explode. If the
conversion is delayed the energy released can power a Gamma Ray Burst. A delay
between the Supernova and the subsequent Gamma Ray Burst is possible, in
agreement with the delay proposed in recent analysis of astrophysical data.Comment: 4 pages, 2 figures. To be published in Phys.Rev.
Optically opaque color-flavor locked phase inside compact stars
The contribution of thermally excited electron-positron pairs to the bulk
properties of the color-flavor locked quark phase inside compact stars is
examined. The presence of these pairs causes the photon mean free path to be
much smaller than a typical core radius ( km) for all
temperatures above 25 keV so that the photon contribution to the thermal
conductivity is much smaller than that of the Nambu-Goldstone bosons. We also
find that the electrons and positrons dominate the electrical conductivity,
while their contributions to the total thermal energy is negligible.Comment: 3 pages, 2 figures. Published versio
Strange Stars with a Density-Dependent Bag Parameter
We have studied strange quark stars in the framework of the MIT bag model,
allowing the bag parameter B to depend on the density of the medium. We have
also studied the effect of Cooper pairing among quarks, on the stellar
structure. Comparison of these two effects shows that the former is generally
more significant. We studied the resulting equation of state of the quark
matter, stellar mass-radius relation, mass-central-density relation,
radius-central-density relation, and the variation of the density as a function
of the distance from the centre of the star. We found that the
density-dependent B allows stars with larger masses and radii, due to
stiffening of the equation of state. Interestingly, certain stellar
configurations are found to be possible only if B depends on the density. We
have also studied the effect of variation of the superconducting gap parameter
on our results.Comment: 23 pages, 8 figs; v2: 25 pages, 9 figs, version to be published in
Phys. Rev. (D
Detecting local synchronization in coupled chaotic systems
We introduce a technique to detect and quantify local functional dependencies
between coupled chaotic systems. The method estimates the fraction of locally
syncronized configurations, in a pair of signals with an arbitrary state of
global syncronization. Application to a pair of interacting Rossler oscillators
shows that our method is capable to quantify the number of dynamical
configurations where a local prediction task is possible, also in absence of
global synchronization features
Global Strings in High Density QCD
We show that several types of global strings occur in colour superconducting
quark matter due to the spontaneous violation of relevant U(1) symmetries.
These include the baryon U(1)_B, and approximate axial U(1)_A symmetries as
well as an approximate U(1)_S arising from kaon condensation. We discuss some
general properties of these strings and their interactions. In particular, we
demonstrate that the U(1)_A strings behave as superconducting strings. We draw
some parallels between these strings and global cosmological strings and
discuss some possible implications of these strings to the physics in neutron
star cores.Comment: LaTeX JHEP-format (26 pages) Option in source for REVTeX4 forma
Holographic Nuclear Physics
We analyze the phases of the Sakai-Sugimoto model at finite temperature and
baryon chemical potential. Baryonic matter is represented either by 4-branes in
the 8-branes or by strings stretched from the 8-branes to the horizon. We find
the explicit configurations and use them to determine the phase diagram and
equation of state of the model. The 4-brane configuration (nuclear matter) is
always preferred to the string configuration (quark matter), and the latter is
also unstable to density fluctuations. In the deconfined phase the phase
diagram has three regions corresponding to the vacuum, quark-gluon plasma, and
nuclear matter, with a first-order and a second-order phase transition
separating the phases. We find that for a large baryon number density, and at
low temperatures, the dominant phase has broken chiral symmetry. This is in
qualitative agreement with studies of QCD at high density.Comment: 27 pages, 26 figures. v2: Added a comment about higher derivative
corrections to the DBI action in the smeared instanton in section 2.1. v3:
References added, version published in JHEP. v4: misprints correcte
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