2,312 research outputs found
Viscous damping of r-modes: Large amplitude saturation
We analyze the viscous damping of r-mode oscillations of compact stars,
taking into account non-linear viscous effects in the large-amplitude regime.
The qualitatively different cases of hadronic stars, strange quark stars, and
hybrid stars are studied. We calculate the viscous damping times of r-modes,
obtaining numerical results and also general approximate analytic expressions
that explicitly exhibit the dependence on the parameters that are relevant for
a future spindown evolution calculation. The strongly enhanced damping of large
amplitude oscillations leads to damping times that are considerably lower than
those obtained when the amplitude dependence of the viscosity is neglected.
Consequently, large-amplitude viscous damping competes with the gravitational
instability at all physical frequencies and could stop the r-mode growth in
case this is not done before by non-linear hydrodynamic mechanisms.Comment: 18 pages, 17 figures, changed convention for the r-mode amplitude,
version to be published in PR
Ginzburg-Landau approach to the three flavor LOFF phase of QCD
We explore, using a Ginzburg-Landau expansion of the free energy, the
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of QCD with three flavors, using
the NJL four-fermion coupling to mimic gluon interactions. We find that, below
the point where the QCD homogeneous superconductive phases should give way to
the normal phase, Cooper condensation of the pairs u-s and d-u is possible, but
in the form of the inhomogeneous LOFF pairing.Comment: 8 pages, 4 figures. Eq. (20) corrected. As a consequence figures have
been modified to show only the solution with parallel total momenta of the
us, ud pairs, as the other configurations are suppressed. Main conclusions of
the paper are unchange
A diagrammatic derivation of the meson effective masses in the neutral color-flavor-locked phase of Quantum Chromodynamics
We offer a diagrammatic derivation of the effective masses of the axial
flavor excitations in the electrical and color neutral CFL phase of QCD. In
particular we concentrate on the excitations with the quantum numbers of the
kaons: we show how their effective chemical potentials, responsible of their
Bose-Einstein condensation and found previously on the basis of pure symmetry
arguments, arise at the microscopic level by loop effects. We perform also the
numerical evaluation of the relevant loops in the whole CFL regime
, showing the existence of the enhancement of the
kaon condensation with respect to the lowest order result. Finally we discuss
the role of electrical and color neutrality in the microscopic calculation.Comment: 10 pages, 2 figures, RevTeX4 style. Version accepted for publication
on JHEP. Some minor change in the tex
Dense quark matter in compact stars
The densest predicted state of matter is colour-superconducting quark matter,
in which quarks near the Fermi surface form a condensate of Cooper pairs. This
form of matter may well exist in the core of compact stars, and the search for
signatures of its presence is an ongoing enterprise. Using a bag model of quark
matter, I discuss the effects of colour superconductivity on the mass-radius
relationship of compact stars, showing that colour superconducting quark matter
can occur in compact stars at values of the bag constant where ordinary quark
matter would not be allowed. The resultant ``hybrid'' stars with colour
superconducting quark matter interior and nuclear matter surface have masses in
the range 1.3-1.6 Msolar and radii 8-11 km. Once perturbative corrections are
included, quark matter can show a mass-radius relationship very similar to that
of nuclear matter, and the mass of a hybrid star can reach 1.8 \Msolar.Comment: 11 pages, for proceedings of SQM 2003 conference; references added,
abstract reworde
Nonlocality effects on Color Spin Locking condensates
We consider the color spin locking (CSL) phase of two-flavor quark matter at
zero temperature for nonlocal instantaneous, separable interactions. We employ
a Lorentzian-type form factor allowing a parametric interpolation between the
sharp (Nambu-Jona-Lasinio (NJL) model) and very smooth (e.g. Gaussian) cut-off
models for systematic studies of the influence on the CSL condensate the
deviation from the NJL model entails. This smoothing of the NJL model form
factor shows advantageous features for the phenomenology of compact stars: (i)
a lowering of the critical chemical potential for the onset of the chiral phase
transition as a prerequisite for stability of hybrid stars with extended quark
matter cores and (ii) a reduction of the smallest pairing gap to the order of
100 keV, being in the range of values interesting for phenomenological studies
of hybrid star cooling evolution.Comment: 8 pages, 8 figures, 1 table, accepted for publication in Phys.Rev.
Mass-Induced Crystalline Color Superconductivity
We demonstrate that crystalline color superconductivity may arise as a result
of pairing between massless quarks and quarks with nonzero mass m_s. Previous
analyses of this phase of cold dense quark matter have all utilized a chemical
potential difference \delta\mu to favor crystalline color superconductivity
over ordinary BCS pairing. In any context in which crystalline color
superconductivity occurs in nature, however, it will be m_s-induced. The effect
of m_s is qualitatively different from that of \delta\mu in one crucial
respect: m_s depresses the value of the BCS gap \Delta_0 whereas \delta\mu
leaves \Delta_0 unchanged. This effect in the BCS phase must be taken into
account before m_s-induced and \delta\mu-induced crystalline color
superconductivity can sensibly be compared.Comment: 12 pages, 4 figures. v2: very small change onl
Color-flavor locked strangelets in a quark mass density-dependent model
The color-flavor locked (CFL) phase of strangelets is investigated in a quark
mass density-dependent model. Parameters are determined by stability arguments.
It is concluded that three solutions to the system equations can be found,
corresponding, respectively, to positively charged, negatively charged, and
nearly neutral CFL strangelets. The charge to baryon number of the positively
charged strangelets is smaller than the previous result, while the charge of
the negatively charged strangelets is nearly proportional in magnitude to the
cubic-root of the baryon number. However, the positively charged strangelets
are more stable compared to the other two solutions.Comment: 11 pages,7 figures, Accepted for publication in Int. J. Mod. Phys.
Internal Frame Dragging and a Global Analog of the Aharonov-Bohm Effect
It is shown that the breakdown of a {\it global} symmetry group to a discrete
subgroup can lead to analogues of the Aharonov-Bohm effect. At sufficiently low
momentum, the cross-section for scattering of a particle with nontrivial
charge off a global vortex is almost equal to (but definitely different from)
maximal Aharonov-Bohm scattering; the effect goes away at large momentum. The
scattering of a spin-1/2 particle off a magnetic vortex provides an amusing
experimentally realizable example.Comment: (14 pp
Gapless color-flavor locked phase in quark and hybrid stars
We study the effects of the gapless color-flavor locked (gCFL) phase on the
equation of state of strongly interacting matter in the range of baryonic
chemical potential involved in a compact star. We analyze the possibility of a
phase transition from hadronic matter to gCFL quark matter and we discuss, for
different values of the strange quark mass and diquark coupling strength, the
existence of a gCFL phase in quark or hybrid stars. The mass-radius relation
and the structure of compact stars containing the gCFL phase are shown and the
physical relevance of this superconducting phase inside a stellar object is
also discussed.Comment: 7 pages, 11 figure
Bulk viscosity in the nonlinear and anharmonic regime of strange quark matter
The bulk viscosity of cold, dense three-flavor quark matter is studied as a
function of temperature and the amplitude of density oscillations. The study is
also extended to the case of two different types of anharmonic oscillations of
density. We point several qualitative effects due to the anharmonicity,
although quantitatively they appear to be relatively small. We also find that,
in most regions of the parameter space, with the exception of the case of a
very large amplitude of density oscillations (i.e. 10% and above), nonlinear
effects and anharmonicity have a small effect on the interplay of the
nonleptonic and semileptonic processes in the bulk viscosity.Comment: 14 pages, 6 figures; v2: Appendix B is omitted, a few new discussions
added and some new references adde
- …