2,773 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
Nonlocality effects on spin-one pairing patterns in two-flavor color superconducting quark matter and compact stars applications
We study the influence of nonlocality in the interaction on two spin one
pairing patterns of two-flavor quark matter: the anisotropic blue color paring
besides the usual two color superconducting matter (2SCb), in which red and
green colors are paired, and the color spin locking phase (CSL). The effect of
nonlocality on the gaps is rather large and the pairings exhibit a strong
dependence on the form factor of the interaction, especially in the low density
region. The application of these small spin-one condensates for compact stars
is analyzed: the early onset of quark matter in the nonlocal models may help to
stabilize hybrid star configurations. While the anisotropic blue quark pairing
does not survive a big asymmetry in flavor space as imposed by the charge
neutrality condition, the CSL phase as a flavor independent pairing can be
realized as neutral matter in compact star cores. However, smooth form factors
and the missmatch between the flavor chemical potential in neutral matter make
the effective gaps of the order of magnitude keV, and a more
systematic analysis is needed to decide whether such small gaps could be
consistent with the cooling phenomenology.Comment: 18 pages, 7 figures, corrected version with revised parameterizatio
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.
Effects of quark matter and color superconductivity in compact stars
The equation of state for quark matter is derived for a nonlocal, chiral
quark model within the mean field approximation. We investigate the effects of
a variation of the form factors of the interaction on the phase diagram of
quark matter under the condition of beta-equilibrium and charge neutrality.
Special emphasis is on the occurrence of a diquark condensate which signals a
phase transition to color superconductivity and its effects on the equation of
state. We calculate the quark star configurations by solving the Tolman-
Oppenheimer- Volkoff equations and obtain for the transition from a hot, normal
quark matter core of a protoneutron star to a cool diquark condensed one a
release of binding energy of the order of Delta M c^2 ~ 10^{53} erg. We study
the consequences of antineutrino trapping in hot quark matter for quark star
configurations with possible diquark condensation and discuss the claim that
this energy could serve as an engine for explosive phenomena. A "phase diagram"
for rotating compact stars (angular velocity-baryon mass plane) is suggested as
a heuristic tool for obtaining constraints on the equation of state of QCD at
high densities. It has a critical line dividing hadronic from quark core stars
which is correlated with a local maximum of the moment of inertia and can thus
be subject to experimental verification by observation of the rotational
behavior of accreting compact stars.Comment: 14 pages, 12 figures, Talk given at 2nd International Workshop on
Hadron Physics: Effective Theories of Low-Energy QCD, Coimbra, Portugal,
25-29 Sep 200
Energy release due to antineutrino untrapping and diquark condensation in hot quark star evolution
We study the consequences of antineutrino trapping in hot quark matter for
quark star configurations with possible diquark condensation. Due to the
conditions of charge neutrality and beta-equilibrium the flavor asymmetry
increases with the number density of trapped antineutrinos such that above a
critical value of the antineutrino chemical potential of 30 MeV diquark
condensation is inhibited. When the quark star cools a two-phase structure
occurs: a superconducting quark matter core surrounded by a shell of normal
quark matter. Below the critical temperature of about 1 MeV, the antineutrino
mean free path becomes larger than the thickness of the normal quark matter
shell so that they get untrapped within a sudden process. By comparing the
masses of configurations with the same baryon number we estimate that the
release of energy due to the antineutrino untrapping transition can be in the
range of 10^{51} to 10^{52} erg.Comment: 7 pages, 5 figures, uses aa.cls (included), numerical results
updated, reference added, minor text modification
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
A synthetic population of Wolf-Rayet stars in the LMC based on detailed single and binary star evolution models
Without doubt, mass transfer in close binary systems contributes to the
populations of Wolf-Rayet (WR) stars in the Milky Way and the Magellanic
Clouds. However, the binary formation channel is so far not well explored. We
want to remedy this by exploring large grids of detailed binary and single star
evolution models computed with the publicly available MESA code, for a
metallicity appropriate for the Large Magellanic Cloud (LMC). The binary models
are calculated through Roche-lobe overflow and mass transfer, until the
initially more massive star exhausts helium in its core. We distinguish models
of WR and helium stars based on the estimated stellar wind optical depth. We
use these models to build a synthetic WR population, assuming constant star
formation. Our models can reproduce the WR population of the LMC to significant
detail, including the number and luminosity functions of the main WR subtypes.
We find that for binary fractions of 100% (50%), all LMC WR stars below
() are stripped binary mass donors. We
also identify several insightful mismatches. With a single star fraction of
50\%, our models produce too many yellow supergiants, calling either for a
larger initial binary fraction, or for enhanced mass-loss near the
Humphreys-Davidson limit. Our models predict more long-period WR binaries than
observed, arguably due to an observational bias towards short periods. Our
models also underpredict the shortest-period WR binaries, which may have
implications for understanding the progenitors of double black hole mergers.
The fraction of binary produced WR stars may be larger than often assumed, and
outline the risk to mis-calibrate stellar physics when only single star models
are used to reproduce the observed WR stars.Comment: 15 pages + 13 pages appendix, 14 figures, 2 table
A basis for variational calculations in d dimensions
In this paper we derive expressions for matrix elements (\phi_i,H\phi_j) for
the Hamiltonian H=-\Delta+\sum_q a(q)r^q in d > 1 dimensions.
The basis functions in each angular momentum subspace are of the form
phi_i(r)=r^{i+1+(t-d)/2}e^{-r^p/2}, i >= 0, p > 0, t > 0. The matrix elements
are given in terms of the Gamma function for all d. The significance of the
parameters t and p and scale s are discussed. Applications to a variety of
potentials are presented, including potentials with singular repulsive terms of
the form b/r^a, a,b > 0, perturbed Coulomb potentials -D/r + B r + Ar^2, and
potentials with weak repulsive terms, such as -g r^2 + r^4, g > 0.Comment: 22 page
The SuperMACHO Microlensing Survey
We present the first results from our next-generation microlensing survey,
the SuperMACHO project. We are using the CTIO 4m Blanco telescope and the
MOSAIC imager to carry out a search for microlensing toward the Large
Magellanic Cloud (LMC). We plan to ascertain the nature of the population
responsible for the excess microlensing rate seen by the MACHO project. Our
observing strategy is optimized to measure the differential microlensing rate
across the face of the LMC. We find this derivative to be relatively
insensitive to the details of the LMC's internal structure but a strong
discriminant between Galactic halo and LMC self lensing. In December 2003 we
completed our third year of survey operations. 2003 also marked the first year
of real-time microlensing alerts and photometric and spectroscopic followup. We
have extracted several dozen microlensing candidates, and we present some
preliminary light curves and related information. Similar to the MACHO project,
we find SNe behind the LMC to be a significant contaminant - this background
has not been completely removed from our current single-color candidate sample.
Our follow-up strategy is optimized to discriminate between SNe and true
microlensing.Comment: To appear in Proceedings of IAU Symposium 225: Impact of
Gravitational Lensing on Cosmology, 6 page
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