150 research outputs found
Rapid cooling of magnetized neutron stars
The neutrino emissivities resulting from direct URCA processes in neutron
stars are calculated in a relativistic Dirac-Hartree approach in presence of a
magnetic field. In a quark or a hyperon matter environment, the emissivity due
to nucleon direct URCA processes is suppressed relative to that from pure
nuclear matter. In all the cases studied, the magnetic field enhances
emissivity compared to the field-free cases.Comment: 9 pages; Revtex; figure include
Antikaon condensation and the metastability of protoneutron stars
We investigate the condensation of meson along with
condensation in the neutrino trapped matter with and without hyperons.
Calculations are performed in the relativistic mean field models in which both
the baryon-baryon and (anti)kaon-baryon interactions are mediated by meson
exchange. In the neutrino trapped matter relevant to protoneutron stars, the
critical density of condensation is shifted considerably to higher
density whereas that of condensation is shifted slightly to higher
density with respect to that of the neutrino free case. The onset of
condensation always occurs earlier than that of condensation. A
significant region of maximum mass protoneutron stars is found to contain condensate for larger values of the antikaon potential. With the
appearance of condensation, there is a region of symmetric nuclear
matter in the inner core of a protoneutron star. It is found that the maximum
mass of a protoneutron star containing and condensate is
greater than that of the corresponding neutron star. We revisit the implication
of this scenario in the context of the metastability of protoneutron stars and
their evolution to low mass black holes.Comment: 26 pages; Revtex; 8 figures include
Chiral Restoration in Hot and/or Dense Matter
Chiral restoration phase transition in hot and/or dense hadronic matter is
discussed in terms of the BR scaling based on chiral symmetry and scale anomaly
of QCD. The precise connection between the scalar field that figures in the
trace anomaly and the sigma field that figures in the linear model is
established. It is suggested that in hot and/or dense medium, the nonlinear
model linearizes with the help of a dilaton to a linear model
with medium-renormalized constants. The relevance of Georgi's vector symmetry
and/or Weinberg's ``mended symmetry" in chiral restoration is pointed out. Some
striking consequences for relativistic heavy-ion collisions and dense matter in
compact stars following stellar collapse are discussed.Comment: 66 pages, Latex, 19 figures (not included, available on request),
Prepared for Physics Report
Dynamics of spherically symmetric spacetimes: hydrodynamics and radiation
Using the 3+1 formalism of general relativity we obtain the equations
governing the dynamics of spherically symmetric spacetimes with arbitrary
sources. We then specialize for the case of perfect fluids accompanied by a
flow of interacting massless or massive particles (e.g. neutrinos) which are
described in terms of relativistic transport theory. We focus in three types of
coordinates: 1) isotropic gauge and maximal slicing, 2) radial gauge and polar
slicing, and 3) isotropic gauge and polar slicing.Comment: submitted to Phys. Rev. D, 46 pages, RevTex file, no figure
Neutron star properties in the quark-meson coupling model
The effects of internal quark structure of baryons on the composition and
structure of neutron star matter with hyperons are investigated in the
quark-meson coupling (QMC) model. The QMC model is based on mean-field
description of nonoverlapping spherical bags bound by self-consistent exchange
of scalar and vector mesons. The predictions of this model are compared with
quantum hadrodynamic (QHD) model calibrated to reproduce identical nuclear
matter saturation properties. By employing a density dependent bag constant
through direct coupling to the scalar field, the QMC model is found to exhibit
identical properties as QHD near saturation density. Furthermore, this modified
QMC model provides well-behaved and continuous solutions at high densities
relevant to the core of neutron stars. Two additional strange mesons are
introduced which couple only to the strange quark in the QMC model and to the
hyperons in the QHD model. The constitution and structure of stars with
hyperons in the QMC and QHD models reveal interesting differences. This
suggests the importance of quark structure effects in the baryons at high
densities.Comment: 28 pages, 10 figures, to appear in Physical Review
Magnetic Field Generation in Stars
Enormous progress has been made on observing stellar magnetism in stars from
the main sequence through to compact objects. Recent data have thrown into
sharper relief the vexed question of the origin of stellar magnetic fields,
which remains one of the main unanswered questions in astrophysics. In this
chapter we review recent work in this area of research. In particular, we look
at the fossil field hypothesis which links magnetism in compact stars to
magnetism in main sequence and pre-main sequence stars and we consider why its
feasibility has now been questioned particularly in the context of highly
magnetic white dwarfs. We also review the fossil versus dynamo debate in the
context of neutron stars and the roles played by key physical processes such as
buoyancy, helicity, and superfluid turbulence,in the generation and stability
of neutron star fields.
Independent information on the internal magnetic field of neutron stars will
come from future gravitational wave detections. Thus we maybe at the dawn of a
new era of exciting discoveries in compact star magnetism driven by the opening
of a new, non-electromagnetic observational window.
We also review recent advances in the theory and computation of
magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo
theory. These advances offer insight into the action of stellar dynamos as well
as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field
generation in stars to appear in Space Science Reviews, Springe
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
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