22 research outputs found
Massive charged particle's tunneling from spherical charged black hole
We generalize the Parikh-Wilczek scheme to the tunneling of a massive charged
particle from a general spherical charged black hole. We obtain that the
tunneling probability depends on the energy, the mass and the charge of the
particle. In particular, the modified Hawking temperature is related to the
charge. Only at the leading order approximation can the standard Hawking
temperature be reproduced. We take the Reissner-Nordstr\"{o}m black hole as an
example to clarify our points of view, and find that the accumulation of
Hawking radiation makes it approach an extreme black hole.Comment: 10 pages, no figures; v2: a minor typo corrected; v3: 11 pages,
clarification and reference added, final version to be published in EPL; v4:
minor modifications to match the published versio
On tunneling across horizons
The tunneling method for stationary black holes in the Hamilton-Jacobi
variant is reconsidered in the light of various critiques that have been moved
against. It is shown that once the tunneling trajectories have been correctly
identified the method isfree from internal inconsistencies, it is manifestly
covariant, it allows for the extension to spinning particles and it can even be
used without solving the Hamilton-Jacobi equation. These conclusions borrow
support on a simple analytic continuation of the classical action of a
pointlike particle, made possible by the unique assumption that it should be
analytic in complexified Schwarzschild or Kerr-Newman spacetimes. A more
general version of the Parikh-Wilczek method will also be proposed along these
lines.Comment: Latex Document, 5 pages, 2 figures, title changed, abstract changed,
added references, results unchange
Glassy Phase Transition and Stability in Black Holes
Black hole thermodynamics, confined to the semi-classical regime, cannot
address the thermodynamic stability of a black hole in flat space. Here we show
that inclusion of correction beyond the semi-classical approximation makes a
black hole thermodynamically stable. This stability is reached through a phase
transition. By using Ehrenfest's scheme we further prove that this is a glassy
phase transition with a Prigogine-Defay ratio close to 3. This value is well
placed within the desired bound (2 to 5) for a glassy phase transition. Thus
our analysis indicates a very close connection between the phase transition
phenomena of a black hole and glass forming systems. Finally, we discuss the
robustness of our results by considering different normalisations for the
correction term.Comment: v3, minor changes over v2, references added, LaTeX-2e, 18 pages, 3 ps
figures, to appear in Eour. Phys. Jour.
A 43-GHz Survey in the ELAIS N2 Area
We describe a survey in the ELAIS N2 region with the VLA at 43.4 GHz, carried
out with 1627 independent snapshot observations in D-configuration and covering
about 0.5 square degrees. One certain source is detected, a
previously-catalogued flat-spectrum QSO at z=2.2. A few (<5) other sources may
be present at about the 3sigma level, as determined from positions of
source-like deflections coinciding with blue stellar objects, or with sources
from lower-frequency surveys. Independently we show how all the source-like
detections identified in the data can be used with a maximum-likelihood
technique to constrain the 43-GHz source counts at a level of ~7 mJy. Previous
estimates of the counts at 43 GHz, based on lower-frequency counts and spectral
measurements, are consistent with these constraints, although the present
results are suggestive of somewhat higher surface densities at the 7 mJy level.
They do not provide direct evidence of intrusion of a previously unknown source
population, although the several candidate sources need examination before such
a population can be ruled out.Comment: 13 pages, 11 figures, 1 table; accepted for publication in Mon. Not
R. Astr. So
Observer Dependent Horizon Temperatures: a Coordinate-Free Formulation of Hawking Radiation as Tunneling
We reformulate the Hamilton-Jacobi tunneling method for calculating Hawking
radiation in static, spherically-symmetric spacetimes by explicitly
incorporating a preferred family of frames. These frames correspond to a family
of observers tied to a locally static timelike Killing vector of the spacetime.
This formulation separates the role of the coordinates from the choice of
vacuum and thus provides a coordinate-independent formulation of the tunneling
method. In addition, it clarifies the nature of certain constants and their
relation to these preferred observers in the calculation of horizon
temperatures. We first use this formalism to obtain the expected temperature
for a static observer at finite radius in the Schwarzschild spacetime. We then
apply this formalism to the Schwarzschild-de Sitter spacetime, where there is
no static observer with 4-velocity equal to the static timelike Killing vector.
It is shown that a preferred static observer, one whose trajectory is geodesic,
measures the lowest temperature from each horizon. Furthermore, this observer
measures horizon temperatures corresponding to the well-known Bousso-Hawking
normalization.Comment: 11 pages, 1 2-part figure, references added, appendix added,
discussion streamline
Fermions and Kaluza-Klein vacuum decay: a toy model
We address the question of whether or not fermions with twisted periodicity
condition suppress the semiclassical decay of M^4xS^1 Kaluza--Klein vacuum. We
consider a toy (1+1)-dimensional model with twisted fermions in cigar-shaped
Euclidean background geometry and calculate the fermion determinant. We find
that contrary to expectations, the determinant is finite. We consider this as
an indication that twisted fermions do not stabilize the Kaluza--Klein vacuum.Comment: 13 pages, 2 figure
Hamilton-Jacobi Tunneling Method for Dynamical Horizons in Different Coordinate Gauges
Previous work on dynamical black hole instability is further elucidated
within the Hamilton-Jacobi method for horizon tunneling and the reconstruction
of the classical action by means of the null-expansion method. Everything is
based on two natural requirements, namely that the tunneling rate is an
observable and therefore it must be based on invariantly defined quantities,
and that coordinate systems which do not cover the horizon should not be
admitted. These simple observations can help to clarify some ambiguities, like
the doubling of the temperature occurring in the static case when using
singular coordinates, and the role, if any, of the temporal contribution of the
action to the emission rate. The formalism is also applied to FRW cosmological
models, where it is observed that it predicts the positivity of the temperature
naturally, without further assumptions on the sign of the energy.Comment: Standard Latex document, typos corrected, refined discussion of
tunneling picture, subsection 5.1 remove
A General Black String and its Microscopics
Using G2(2) dualities we construct the most general black string solution of
minimal five-dimensional ungauged supergravity. The black string has five
independent parameters, namely, the magnetic one-brane charge, smeared electric
zero-brane charge, boost along the string direction, energy above the BPS
bound, and rotation in the transverse space. In one extremal limit it reduces
to the three parameter supersymmetric string of five-dimensional minimal
supergravity; in another extremal limit it reduces to the three parameter
non-supersymmetric extremal string of five-dimensional minimal supergravity. It
also admits an extremal limit when it has maximal rotation in the
four-dimensional transverse space. The decoupling limit of our general black
string is a BTZ black hole times a two sphere. The macroscopic entropy of the
string is reproduced by the Maldacena-Strominger-Witten CFT in appropriate
ranges of the parameters. When the pressureless condition is imposed, our
string describes the infinite radius limit of the most general class of black
rings of minimal supergravity. We discuss implications our solution has for
extremal and non-extremal black rings of minimal supergravity.Comment: 35 pages; 3 figures; v2 section 4.1.1 rewritten + minor changes + ref
adde
Shaping black holes with free fields
Starting from a metric Ansatz permitting a weak version of Birkhoff's theorem
we find static black hole solutions including matter in the form of free scalar
and p-form fields, with and without a cosmological constant \Lambda. Single
p-form matter fields permit multiple possibilities, including dyonic solutions,
self-dual instantons and metrics with Einstein-Kaelher horizons. The inclusion
of multiple p-forms on the other hand, arranged in a homogeneous fashion with
respect to the horizon geometry, permits the construction of higher dimensional
dyonic p-form black holes and four dimensional axionic black holes with flat
horizons, when \Lambda<0. It is found that axionic fields regularize black hole
solutions in the sense, for example, of permitting regular -- rather than
singular -- small mass Reissner-Nordstrom type black holes. Their cosmic string
and Vaidya versions are also obtained.Comment: 38 pages. v2: minor changes, published versio
Dynamical Boson Stars
The idea of stable, localized bundles of energy has strong appeal as a model
for particles. In the 1950s John Wheeler envisioned such bundles as smooth
configurations of electromagnetic energy that he called {\em geons}, but none
were found. Instead, particle-like solutions were found in the late 1960s with
the addition of a scalar field, and these were given the name {\em boson
stars}. Since then, boson stars find use in a wide variety of models as sources
of dark matter, as black hole mimickers, in simple models of binary systems,
and as a tool in finding black holes in higher dimensions with only a single
killing vector. We discuss important varieties of boson stars, their dynamic
properties, and some of their uses, concentrating on recent efforts.Comment: 79 pages, 25 figures, invited review for Living Reviews in
Relativity; major revision in 201