2,659 research outputs found
Neutral color-spin locking phase in neutron stars
We present results for the spin-1 color-spin locking phase (CSL) using a
NJL-type model in two flavor quark matter for compact stars applications. The
CSL condensate is flavor symmetric and therefore charge and color neutrality
can easily be satisfied. We find small energy gaps ~1 MeV, which make the CSL
matter composition and the EoS not very different from the normal quark matter
phase. We keep finite quark masses in our calculations and obtain no gapless
modes that could have strong consequences in the late cooling of neutron stars.
Finally, we show that the region of the phase diagram relevant for neutron star
cores, when asymmetric flavor pairing is suppressed, could be covered by the
CSL phase.Comment: 3 pages, 4 figures, contribution talk to the IVth International
Conference on Quarks and Nuclear Physics(QNP06), Madrid, Spain, 5-10 Jun 200
A BCS Gap on the Lattice
Monte Carlo simulations of the 3+1 dimensional NJL model are performed with
baryon chemical potential mu>0. For mu>Sigma_0, the constituent quark mass in
vacuum, chiral symmetry is restored and a diquark condensate forms. We
analyse the fermion propagator and find evidence for particle-hole mixing in
the vicinity of the Fermi surface and an energy gap Delta>0, both of which
provide evidence for superfluidity at high baryon density induced by a BCS
mechanism.
At (mu a)=0.8 the ratio between the BCS gap and the vacuum quark mass is
Delta/Sigma_0=0.15(2).Comment: 3 pages, 3 figures, Lattice2003(nonzero
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
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
Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds
<p>A series of Ba<sub>1-x-y</sub>Sr<sub>x</sub>Ca<sub>y</sub>TiO<sub>3</sub> compounds were prepared with varying average ionic radii and cation disorder on A-site. All samples showed typical ferroelectric behavior. A simple empirical equation correlated Curie temperature, <em>T<sub>C</sub></em>, with the values of ionic radii of A-site cations. This correlation was related to the distortion of TiO<sub>6</sub> octahedra observed during neutron diffraction studies. The equation was used for the selection of compounds with predetermined values of <em>T<sub>C</sub></em>. The effects of A-site ionic radii on the temperatures of phase transitions in Ba<sub>1-x-y</sub>Sr<sub>x</sub>Ca<sub>y</sub>TiO<sub>3</sub> were discussed. </p
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.
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.
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
Bridging the gap by shaking superfluid matter
In cold compact stars, Cooper pairing between fermions in dense matter leads
to the formation of a gap in their excitation spectrum and typically
exponentially suppresses transport properties. However, we show here that weak
Urca reactions become strongly enhanced and approach their ungapped level when
the star undergoes density oscillations of sufficiently large amplitude. We
study both the neutrino emissivity and the bulk viscosity due to direct Urca
processes in hadronic, hyperonic and quark matter and discuss different
superfluid and superconducting pairing patterns.Comment: 5 pages, 4 figure
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
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