869 research outputs found
Bulk Emission of Scalars by a Rotating Black Hole
We study in detail the scalar-field Hawking radiation emitted into the bulk by a higher-dimensional, rotating black hole. We numerically compute the angular eigenvalues, and solve the radial equation of motion in order to find transmission factors. The latter are found to be enhanced by the angular momentum of the black hole, and to exhibit the well-known effect of superradiance. The corresponding power spectra for scalar fields show an enhancement with the number of dimensions, as in the non-rotating case. On the other hand, the proportion of the total (i.e., bulk+brane) power that is emitted into the bulk decreases monotonically with the angular momentum. We compute the total mass loss rate of the black hole for a variety of black-hole angular momenta and bulk dimensions, and find that, in all cases, the bulk emission remains significantly smaller than the brane emission. The angular-momentum loss rate is also computed and found to have a smaller value in the bulk than on the brane
Scalar Emission in the Bulk in a Rotating Black Hole Background
We study the emission of scalars into the bulk from a higher-dimensional
rotating black hole. We obtain an analytic solution to the field equation by
employing matching techniques on expressions valid in the near-horizon and
far-field regimes. Both analytic and numerical results for the absorption
probability, in the low-energy and low-angular momentum limit, are derived and
found to be in excellent agreement. We also compute the energy emission rate,
and show that the brane-to-bulk ratio of the energy emission rates for scalar
fields remains always larger than unity in the aforementioned regime.Comment: 14 pages, Latex file, 5 figures, references adde
A Comparative Study Between a Micromechanical Cantilever Resonator and MEMS-based Passives for Band-pass Filtering Application
Over the past few years, significant growth has been observed in using MEMS
based passive components in the RF microelectronics domain, especially in
transceiver components. This is due to some excellent properties of the MEMS
devices like low loss, excellent isolation etc. in the microwave frequency
domain where the on-chip passives normally tend to become leakier and degrades
the transceiver performance. This paper presents a comparative analysis between
MEMS-resonator based and MEMS-passives based band-pass filter configurations
for RF applications, along with their design, simulation, fabrication and
characterization. The filters were designed to have a center frequency of 455
kHz, meant for use as the intermediate frequency (IF) filter in superheterodyne
receivers. The filter structures have been fabricated in PolyMUMPs process, a
three-polysilicon layer surface micromachining process.Comment: 6 pages, 15 figure
Exact Results for Evaporating Black Holes in Curvature-Squared Lovelock Gravity: Gauss-Bonnet Greybody Factors
Lovelock gravity is an important extension of General Relativity that
provides a promising framework to study curvature corrections to the Einstein
action, while avoiding ghosts and keeping second order field equations. This
paper derives the greybody factors for D-dimensional black holes arising in a
theory with a Gauss-Bonnet curvature-squared term. These factors describe the
non-trivial coupling between black holes and quantum fields during the
evaporation process: they can be used both from a theoretical viewpoint to
investigate the intricate spacetime structure around such a black hole, and for
phenomenological purposes in the framework of braneworld models with a low
Planck scale. We derive exact spectra for the emission of scalar, fermion and
gauge fields emitted on the brane, and for scalar fields emitted in the bulk,
and demonstrate how the Gauss-Bonnet term can change the bulk-to-brane emission
rates ratio in favour of the bulk channel in particular frequency regimes.Comment: 29 pages, Latex file, 11 figures, Data files (greybody factors)
available at http://lpsc.in2p3.fr/ams/greybody/, typos corrected, references
added, version to appear in Phys. Rev.
A study on Quantization Dimension in complete metric spaces
The primary objective of the present paper is to develop the theory of quantization dimension of an invariant measure associated with an iterated function system consisting of finite number of contractive infinitesimal similitudes in a complete metric space. This generalizes the known results on quantization dimension of self-similar measures in the Euclidean space to a complete metric space. In the last part, continuity of quantization dimension is discussed
Bulk Scalar Stabilization of the Radion without Metric Back-Reaction in the Randall-Sundrum Model
Generalizations of the Randall-Sundrum model containing a bulk scalar field
interacting with the curvature through the general coupling are considered. We derive the general form of the effective 4D
potential for the spin-zero fields and show that in the mass matrix the radion
mixes with the Kaluza-Klein modes of the bulk scalar fluctuations. We
demonstrate that it is possible to choose a non-trivial background form
(where is the extra dimension coordinate) for the bulk scalar
field such that the exact Randall-Sundrum metric is preserved (i.e. such that
there is no back-reaction). We compute the mass matrix for the radion and the
KK modes of the excitations of the bulk scalar relative to the background
configuration and find that the resulting mass matrix implies a
non-zero value for the mass of the radion (identified as the state with the
lowest eigenvalue of the scalar mass matrix). We find that this mass is
suppressed relative to the Planck scale by the standard warp factor needed to
explain the hierarchy puzzle, implying that a mass \sim 1\tev is a natural
order of magnitude for the radion mass. The general considerations are
illustrated in the case of a model containing an interaction term.Comment: 22 pages, 3 figure
Goldberger-Wise variations: stabilizing brane models with a bulk scalar
Braneworld scenarios with compact extra-dimensions need the volume of the
extra space to be stabilized. Goldberger and Wise have introduced a simple
mechanism, based on the presence of a bulk scalar field, able to stabilize the
radius of the Randall-Sundrum model. Here, we transpose the same mechanism to
generic single-brane and two-brane models, with one extra dimension and
arbitrary scalar potentials in the bulk and on the branes. The single-brane
construction turns out to be always unstable, independently of the bulk and
brane potentials. In the case of two branes, we derive some generic criteria
ensuring the stabilization or destabilization of the system.Comment: 8 pages, 2 figures. 1 figure and one subsection added. version
published on PR
Do stringy corrections stabilize coloured black holes?
We consider hairy black hole solutions of Einstein-Yang-Mills-Dilaton theory,
coupled to a Gauss-Bonnet curvature term, and we study their stability under
small, spacetime-dependent perturbations. We demonstrate that the stringy
corrections do not remove the sphaleronic instabilities of the coloured black
holes with the number of unstable modes being equal to the number of nodes of
the background gauge function. In the gravitational sector, and in the limit of
an infinitely large horizon, the coloured black holes are also found to be
unstable. Similar behaviour is exhibited by the magnetically charged black
holes while the bulk of the neutral black holes are proven to be stable under
small, gauge-dependent perturbations. Finally, the electrically charged black
holes are found to be characterized only by the existence of a gravitational
sector of perturbations. As in the case of neutral black holes, we demonstrate
that for the bulk of electrically charged black holes no unstable modes arise
in this sector.Comment: 17 pages, Revtex, comments and a reference added, version to appear
in Physical Review
Graviton Emission in the Bulk from a Higher-Dimensional Schwarzschild Black Hole
We consider the evaporation of (4+n)-dimensional non-rotating black holes
into gravitons. We calculate the energy emission rate for gravitons in the bulk
obtaining analytical solutions of the master equation satisfied by all three
types (S,V,T) of gravitational perturbations. Our results, valid in the
low-energy regime, show a vector radiation dominance for every value of n,
while the relative magnitude of the energy emission rate of the subdominant
scalar and tensor radiation depends on n. The low-energy emission rate in the
bulk for gravitons is well below that for a scalar field, due to the absence of
the dominant l=0,1 modes from the gravitational spectrum. Higher partial waves
though may modify this behaviour at higher energies. The calculated low-energy
emission rate, for all types of degrees of freedom decreases with n, although
the full energy emission rate, integrated over all frequencies, is expected to
increase with n, as in the previously studied case of a bulk scalar field.Comment: 17 pages, 2 figures, minor corrections, accepted by Phys. Lett.
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