3,836 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
Inferring neutron stars crust properties from quiescent thermal emission
The observation of thermal emission from isolated neutron stars and the
modeling of the corresponding cooling curves has been very useful to get
information on the properties of matter at very high densities. More recently,
the detection of quiescent thermal emission from neutron stars in low mass
X-ray binary systems after active periods opened a new window to the physics of
matter at lower densities. Here we analyze a few sources that have been
recently monitored and we show how the models can be used to establish
constraints on the crust composition and their transport properties, depending
on the astrophysical scenarios assumed.Comment: 4 pages, 2 figures, Proceedings of the conference "Compact Stars in
the QCD Phase Diagram IV (CSQCD IV)" September 26-30, 2014, Prerow, German
Quiescent thermal emission from neutron stars in LMXBs
We monitored the quiescent thermal emission from neutron stars in low-mass
X-ray binaries after active periods of intense activity in x-rays (outbursts).
The theoretical modeling of the thermal relaxation of the neutron star crust
may be used to establish constraints on the crust composition and transport
properties, depending on the astrophysical scenarios assumed. We numerically
simulated the thermal evolution of the neutron star crust and compared them
with inferred surface temperatures for five sources: MXB 1659-29, KS 1731-260,
EXO 0748-676, XTE J1701-462 and IGR J17480-2446. We find that the evolution of
MXB 1659-29, KS 1731-260 and EXO 0748-676 can be well described within a deep
crustal cooling scenario. Conversely, we find that the other two sources can
only be explained with models beyond crustal cooling. For the peculiar emission
of XTE J1701-462 we propose alternative scenarios such as residual accretion
during quiescence, additional heat sources in the outer crust, and/or thermal
isolation of the inner crust due to a buried magnetic field. We also explain
the very recent reported temperature of IGR J17480-2446 with an additional heat
deposition in the outer crust from shallow sources.Comment: 19 pages, 32 figures, 2 Append., revised version accepted for
publication in Astronomy & Astrophysic
Exploring jet-launching conditions for SFXTs
In the magneto-centrifugal mechanism for jet formation, accreting neutron
stars are assumed to produce relativistic jets only if their surface magnetic
field is weak enough ( G). However, the most common manifestation
of neutron stars are pulsars, whose magnetic field distribution peaks at G. If the neutron star magnetic field has at least this strength
at birth, it must decay considerably before jets can be launched in binary
systems. We study the magnetic field evolution of a neutron star that accretes
matter from the wind of a high-mass stellar companion so that we can constrain
the accretion rate and the impurities in the crust, which are necessary
conditions for jet formation. We solved the induction equation for the
diffusion and convection of the neutron star magnetic field confined to the
crust, assuming spherical accretion in a simpliflied one-dimensional treatment.
We incorporated state-of-the-art microphysics, including consistent thermal
evolution profiles, and assumed two different neutron star cooling scenarios
based on the superfluidity conditions at the core. We find that in this
scenario, magnetic field decay at long timescales is governed mainly by the
accretion rate, while the impurity content and thermal evolution of the neutron
star play a secondary role. For accretion rates
M yr, surface magnetic fields can decay up to four orders of
magnitude in 10 yr, which is the timescale imposed by the evolution
of the high-mass stellar companion in these systems. Based on these results, we
discuss the possibility of transient jet-launching in strong wind-accreting
high-mass binary systems like supergiant fast X-ray transients.Comment: 8 pages, 8 figures. Accepted for publication in A&
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.
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
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
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