5,470 research outputs found
Interior of Distorted Black Holes
We study the interior of distorted static axisymmetric black holes. We obtain
a general interior solution and study its asymptotics both near the horizon and
singularity. As a special example, we apply the obtained results to the case of
the so-called `caged' black holes.Comment: 12 pages, 16 figure
Massless and massive graviton spectra in anisotropic dilatonic braneworld cosmologies
We consider a braneworld model in which an anisotropic brane is embedded in a
dilatonic background. We solve the background solutions and study the behavior
of the perturbations when the universe evolves from an inflationary Kasner
phase to a Minkowski phase. We calculate the massless mode spectrum, and find
that it does not differ from what expected in standard four-dimensional
cosmological models. We then evaluate the spectrum of both light
(ultrarelativistic) and heavy (nonrelativistic) massive modes, and find that,
at high energies, there can be a strong enhancement of the Kaluza-Klein
spectral amplitude, which can become dominant in the total spectrum. The
presence of the dilaton, on the contrary, decrease the relative importance of
the massive modes.Comment: 18 pages, 4 figures, Typos correction
Swift J0525.6+2416 and IGR J04571+4527: two new hard X-ray selected magnetic cataclysmic variables identified with XMM-Newton
IGR J04571+4527 and Swift J0525.6+2416 are two hard X-ray sources detected in
the Swift/BAT and INTEGRAL/IBIS surveys. They were proposed to be magnetic
cataclysmic variables of the Intermediate Polar (IP) type, based on optical
spectroscopy. IGR J04571+4527 also showed a 1218 s optical periodicity,
suggestive of the rotational period of a white dwarf, further pointing towards
an IP classification. We here present detailed X-ray (0.3-10 keV) timing and
spectral analysis performed with XMM-Newton, complemented with hard X-ray
coverage (15-70 keV) from Swift/BAT. These are the first high signal to noise
observations in the soft X-ray domain for both sources, allowing us to identify
the white dwarf X-ray spin period of Swift J0525.6+2416 (226.28 s), and IGR
J04571+4527 (1222.6 s). A model consisting of multi-temperature optically thin
emission with complex absorption adequately fits the broad-band spectrum of
both sources. We estimate a white dwarf mass of about 1.1 and 1.0 solar masses
for IGR J04571+4527 and Swift J0525.6+2416, respectively. The above
characteristics allow us to unambiguously classify both sources as IPs,
confirming the high incidence of this subclass among hard X-ray emitting
Cataclysmic Variables.Comment: 8 pages, 4 figures, 3 tables. Accepted for publication in MNRA
A New Study of the Transition to Uniform Nuclear Matter in Neutron Stars and Supernovae
A comprehensive microscopic study of the properties of bulk matter at
densities just below nuclear saturation g
cm, zero and finite temperature and high neutron fraction, is outlined,
and preliminary results presented. Such matter is expected to exist in the
inner crust of neutron stars and during the core collapse of massive stars with
$M \gtrsim 8M_{\odot}Comment: 4 pages, 2 figures. Participant Contribution at the ``Dense Matter in
Heavy Ion Collisions and Astrophysics" Summer School, JINR, Dubna, Aug. 21 -
Sept. 1, 2006. To be published in PEPAN letter
Gravitational collapse of homogeneous scalar fields
Conditions under which gravity coupled to self interacting scalar field
determines singularity formation are found and discussed. It is shown that,
under a suitable matching with an external space, the boundary, if collapses
completely, may give rise to a naked singularity. Issues related to the
strength of the singularity are discussed.Comment: LaTeX2e; revised versio
Semi-transparent brane-worlds
We study the evolution of a closed Friedmann brane perturbed by the Hawking
radiation escaping a bulk black hole. The semi-transparent brane absorbes some
of the infalling radiation, the rest being transmitted across the brane to the
other bulk region. We characterize the cosmological evolution in terms of the
transmission rate . For small values of a critical-like
behaviour could be observed, when the acceleration due to radiation pressure
and the deceleration induced by the increasing self-gravity of the brane
roughly compensate each other, and cosmological evolution is approximately the
same as without radiation. Lighter (heavier) branes than those with the
critical energy density will recollapse slower (faster). This feature is
obstructed at high values of , where the overall effect of the
radiation is to speed-up the recollapse. We determine the maximal value of the
transmission rate for which the critical-like behaviour is observed. We also
study the effect of transmission on the evolution of different source terms of
the Friedmann equation. We conclude that among all semi-transparent branes the
slowest recollapse occurs for light branes with total absorption.Comment: 15 pages, 8 figure
A note on dilaton gravity with non-smooth potentials
Recent interest in brane world models motivates the investigation of generic
first order dilaton gravity actions, with potentials having some
non-smoothness. We consider two different types of \delta-like contributions in
the action and analyse their effects on the solutions. Furthermore a second
source of non-smoothness arises due to the remaining ambiguities in the
solutions in the separated smooth patches, after fixing all other constants by
matching and asymptotic conditions. If moreover staticity is assumed, we
explicitly construct exact solutions.
With the methods described, for example models with point like sources or
brane world models (where the second source of non-smoothness becomes crucial),
can now be treated as non-smooth dilaton gravity theories.Comment: 10 pages, 1 table; two new references, some typos corrected,
Dedicated to Wolfgang Kummer at the occasion of his Emeritierun
Vacuum Polarization of a Massless Scalar Field in the Background of a Global Monopole with Finite Core
In this paper we analyze the vacuum polarization effects of a massless scalar
field in the background of a global monopole considering a inner structure to
it. Specifically we investigate the effect of its structure on the vacuum
expectation value of the square of the field operator, ,
admitting a non-minimal coupling between the field with the geometry: $\xi
{\cal{R}}\hat{\Phi}^2$. Also we calculate the corrections on the vacuum
expectation value of the energy-momentum tensor, , due to
the inner structure of the monopole. In order to develop these analysis, we
calculate the Euclidean Green function associated with the system for points in
the region outside the core. As we shall see, for specific value of the
coupling parameter , the corrections caused by the inner structure of the
monopole can provide relevant contributions on these vacuum polarizations.Comment: Accepted for publication in Classical and Quantum Gravity. Added
references. 22 pages, 1 figur
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