906 research outputs found
An interpretation for the entropy of a black hole
We investigate the meaning of the entropy carried away by Hawking radiations
from a black hole. We propose that the entropy for a black hole measures the
uncertainty of the information about the black hole forming matter's
precollapsed configurations, self-collapsed configurations, and inter-collapsed
configurations. We find that gravitational wave or gravitational radiation
alone cannot carry all information about the processes of black hole
coalescence and collapse, while the total information locked in the hole could
be carried away completely by Hawking radiation as tunneling
Generalized Second Law of Black Hole Thermodynamics and Quantum Information Theory
We propose a quantum version of a gedanken experiment which supports the
generalized second law of black hole thermodynamics. A quantum measurement of
particles in the region outside of the event horizon decreases the entropy of
the outside matter due to the entanglement of the inside and outside particle
states. This decrease is compensated, however, by the increase in the detector
entropy. If the detector is conditionally dropped into the black hole depending
on the experimental outcome, the decrease of the matter entropy is more than
compensated by the increase of the black hole entropy via the increase of the
black hole mass which is ultimately attributed to the work done by the
measurement.Comment: 5 pages, RevTex, submitted to PR
An improved effective potential for electroweak phase transitions
It is shown that improved potentials and corrected mass terms can be
introduced by using a quadratic source term in the path integral construction
for the effective action. The advantage of doing things this way is that we
avoid ever having to deal with complex propagators in the loop expansion. The
resulting effective action for electroweak phase transitions is similar to the
usual results.Comment: 16 pages, NCL93-TP16, (REVTEX
Black Hole Evaporation in the Presence of a Short Distance Cutoff
A derivation of the Hawking effect is given which avoids reference to field
modes above some cutoff frequency in the free-fall frame
of the black hole. To avoid reference to arbitrarily high frequencies, it is
necessary to impose a boundary condition on the quantum field in a timelike
region near the horizon, rather than on a (spacelike) Cauchy surface either
outside the horizon or at early times before the horizon forms. Due to the
nature of the horizon as an infinite redshift surface, the correct boundary
condition at late times outside the horizon cannot be deduced, within the
confines of a theory that applies only below the cutoff, from initial
conditions prior to the formation of the hole. A boundary condition is
formulated which leads to the Hawking effect in a cutoff theory. It is argued
that it is possible the boundary condition is {\it not} satisfied, so that the
spectrum of black hole radiation may be significantly different from that
predicted by Hawking, even without the back-reaction near the horizon becoming
of order unity relative to the curvature.Comment: 35 pages, plain LaTeX, UMDGR93-32, NSF-ITP-93-2
Vortices and extreme black holes: the question of flux expulsion
It has been claimed that extreme black holes exhibit a phenomenon of flux
expulsion for abelian Higgs vortices, irrespective of the relative width of the
vortex to the black hole. Recent work by two of the authors showed a subtlety
in the treatment of the event horizon, which cast doubt on this claim. We
analyse in detail the vortex/extreme black hole system, showing that while flux
expulsion can occur, it does not do so in all cases. We give analytic proofs
for both expulsion and penetration of flux, in each case deriving a bound for
that behaviour. We also present extensive numerical work backing up, and
refining, these claims, and showing in detail how a vortex can end on a black
hole in all situations. We also calculate the backreaction of the vortex on the
geometry, and comment on the more general vortex-black hole system.Comment: 28 pages revtex, 10 figures, minor changes, reference adde
Dynamical measure and field theory models free of the cosmological constant problem
Summary of abstract Field theory models including gauge theories with SSB are
presented where the energy density of the true vacuum state (TVS) is zero
without fine tuning. The above models are constructed in the gravitational
theory where a measure of integration \Phi in the action is not necessarily
\sqrt{-g} but it is determined dynamically through additional degrees of
freedom. The ratio \Phi/\sqrt{-g} is a scalar field which can be solved in
terms of the matter degrees of freedom due to the existence of a constraint. We
study a few explicit field theory models where it is possible to combine the
solution of the cosmological constant problem with: 1) possibility for
inflationary scenario for the early universe; 2) spontaneously broken gauge
unified theories (including fermions). The models are free from the well known
problem of the usual scalar-tensor theories in what is concerned with the
classical GR tests. The only difference of the field equations in the Einstein
frame from the canonical equations of the selfconsistent system of Einstein's
gravity and matter fields, is the appearance of the effective scalar field
potential which vanishes in TVS without fine tuning.Comment: Extended version of the contribution to the fourth Alexander
Friedmann International Seminar on Gravitation and Cosmology; accepted for
publication in Phys. Rev. D; 31 page
Quantum corrections to the mass of the supersymmetric vortex
We calculate quantum corrections to the mass of the vortex in N=2
supersymmetric abelian Higgs model in (2+1) dimensions. We put the system in a
box and apply the zeta function regularization. The boundary conditions
inevitably violate a part of the supersymmetries. Remaining supersymmetry is
however enough to ensure isospectrality of relevant operators in bosonic and
fermionic sectors. A non-zero correction to the mass of the vortex comes from
finite renormalization of couplings.Comment: Latex, 18 pp; v2 reference added; v3 minor change
Radiating black hole solutions in arbitrary dimensions
We prove a theorem that characterizes a large family of non-static solutions
to Einstein equations in -dimensional space-time, representing, in general,
spherically symmetric Type II fluid. It is shown that the best known
Vaidya-based (radiating) black hole solutions to Einstein equations, in both
four dimensions (4D) and higher dimensions (HD), are particular cases from this
family. The spherically symmetric static black hole solutions for Type I fluid
can also be retrieved. A brief discussion on the energy conditions,
singularities and horizons is provided.Comment: RevTeX 9 pages, no figure
Gravitational field around a screwed superconducting cosmic string in scalar-tensor theories
We obtain the solution that corresponds to a screwed superconducting cosmic
string (SSCS) in the framework of a general scalar-tensor theory including
torsion. We investigate the metric of the SSCS in Brans-Dicke theory with
torsion and analyze the case without torsion. We show that in the case with
torsion the space-time background presents other properties different from that
in which torsion is absent. When the spin vanish, this torsion is a
-gradient and then it propagates outside of the string. We investigate
the effect of torsion on the gravitational force and on the geodesics of a
test-particle moving around the SSCS. The accretion of matter by wakes
formation when a SSCS moves with speed is investigated. We compare our
results with those obtained for cosmic strings in the framework of
scalar-tensor theory.Comment: 22 pages, LaTeX, presented at the "XXII - Encontro Nacional de Fisica
de Particulas e Campos", Sao Lourenco, MG, Brazi
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