4,153 research outputs found
Growing Hair on the extremal black hole
We show that the nonlinear model in an asymptotically
space-time admits a novel local symmetry. The field action is assumed to be
quartic in the nonlinear model fields and minimally coupled to
gravity. The local symmetry transformation simultaneously twists the nonlinear
model fields and changes the space-time metric, and it can be used to
map an extremal black hole to infinitely many hairy black hole solutions.Comment: 11 pages, 1 figure, minor corrections include
Perturbations in the Kerr-Newman Dilatonic Black Hole Background: I. Maxwell waves
In this paper we analyze the perturbations of the Kerr-Newman dilatonic black
hole background. For this purpose we perform a double expansion in both the
background electric charge and the wave parameters of the relevant quantities
in the Newman-Penrose formalism. We then display the gravitational, dilatonic
and electromagnetic equations, which reproduce the static solution (at zero
order in the wave parameter) and the corresponding wave equations in the Kerr
background (at first order in the wave parameter and zero order in the electric
charge). At higher orders in the electric charge one encounters corrections to
the propagations of waves induced by the presence of a non-vanishing dilaton.
An explicit computation is carried out for the electromagnetic waves up to the
asymptotic form of the Maxwell field perturbations produced by the interaction
with dilatonic waves. A simple physical model is proposed which could make
these perturbations relevant to the detection of radiation coming from the
region of space near a black hole.Comment: RevTeX, 36 pages in preprint style, 1 figure posted as a separate PS
file, submitted to Phys. Rev.
New perturbative solutions of the Kerr-Newman dilatonic black hole field equations
This work describes new perturbative solutions to the classical,
four-dimensional Kerr--Newman dilaton black hole field equations. Our solutions
do not require the black hole to be slowly rotating. The unperturbed solution
is taken to be the ordinary Kerr solution, and the perturbation parameter is
effectively the square of the charge-to-mass ratio of the
Kerr--Newman black hole. We have uncovered a new, exact conjugation (mirror)
symmetry for the theory, which maps the small coupling sector to the strong
coupling sector (). We also calculate the gyromagnetic ratio of
the black hole.Comment: Revtex, 27 page
Microfield Dynamics of Black Holes
The microcanonical treatment of black holes as opposed to the canonical
formulation is reviewed and some major differences are displayed. In particular
the decay rates are compared in the two different pictures.Comment: 22 pages, 4 figures, Revtex, Minor change in forma
Can black holes and naked singularities be detected in accelerators?
We study the conditions for the existence of black holes that can be produced
in colliders at TeV-scale if the space-time is higher dimensional. On employing
the microcanonical picture, we find that their life-times strongly depend on
the details of the model. If the extra dimensions are compact (ADD model),
microcanonical deviations from thermality are in general significant near the
fundamental TeV mass and tiny black holes decay more slowly than predicted by
the canonical expression, but still fast enough to disappear almost
instantaneously. However, with one warped extra dimension (RS model),
microcanonical corrections are much larger and tiny black holes appear to be
(meta)stable. Further, if the total charge is not zero, we argue that naked
singularities do not occur provided the electromagnetic field is strictly
confined on an infinitely thin brane. However, they might be produced in
colliders if the effective thickness of the brane is of the order of the
fundamental length scale (~1/TeV).Comment: 6 pages, RevTeX 3, 1 figure and 1 table, important changes and
addition
Noncommutative Quantum Hall Effect and Aharonov-Bohm Effect
We study a system of electrons moving on a noncommutative plane in the
presence of an external magnetic field which is perpendicular to this plane.
For generality we assume that the coordinates and the momenta are both
noncommutative. We make a transformation from the noncommutative coordinates to
a set of commuting coordinates and then we write the Hamiltonian for this
system. The energy spectrum and the expectation value of the current can then
be calculated and the Hall conductivity can be extracted. We use the same
method to calculate the phase shift for the Aharonov-Bohm effect. Precession
measurements could allow strong upper limits to be imposed on the
noncommutativity coordinate and momentum parameters and .Comment: 9 pages, RevTeX4, references added, small changes in the tex
Utilizing the null stream of Einstein Telescope
Among third-generation ground-based gravitational-wave detectors proposed for the next decade, Einstein Telescope provides a unique kind of null stream \unicode{x2014} the signal-free linear combination of data \unicode{x2014} that enables otherwise inaccessible tests of the noise models. We project and showcase challenges in modeling the noise in the 2030-s and how it will affect the performance of third-generation detectors. We find that the null stream of Einstein Telescope is capable of entirely eliminating transient detector glitches that are known to limit current gravitational-wave searches. The techniques we discuss are computationally efficient and do not require a-priori knowledge about glitch models. Furthermore, we show how the null stream can be used to provide an unbiased estimation of the noise power spectrum necessary for online and offline data analyses even with multiple loud signals in band. We overview other approaches to utilizing the null stream. Finally, we comment on the limitations and future challenges of null stream analyses for Einstein Telescope and arbitrary detector networks
Noncommutative Corrections to the Robertson-Walker metric
Upon applying Chamseddine's noncommutative deformation of gravity we obtain
the leading order noncommutative corrections to the Robertson-Walker metric
tensor. We get an isotropic inhomogeneous metric tensor for a certain choice of
the noncommutativity parameters. Moreover, the singularity of the commutative
metric at is replaced by a more involved space-time structure in the
noncommutative theory. In a toy model we construct a scenario where there is no
singularity at at leading order in the noncommutativity parameter.
Although singularities may still be present for nonzero , they need not be
the source of all time-like geodesics and the result resembles a bouncing
cosmology.Comment: 13 page
Theoretical survey of tidal-charged black holes at the LHC
We analyse a family of brane-world black holes which solve the effective
four-dimensional Einstein equations for a wide range of parameters related to
the unknown bulk/brane physics. We first constrain the parameters using known
experimental bounds and, for the allowed cases, perform a numerical analysis of
their time evolution, which includes accretion through the Earth. The study is
aimed at predicting the typical behavior one can expect if such black holes
were produced at the LHC. Most notably, we find that, under no circumstances,
would the black holes reach the (hazardous) regime of Bondi accretion.
Nonetheless, the possibility remains that black holes live long enough to
escape from the accelerator (and even from the Earth's gravitational field) and
result in missing energy from the detectors.Comment: RevTeX4, 12 pages, 4 figures, 5 tables, minor changes to match the
accepted version in JHE
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