69 research outputs found
Proof of universality for the absorption of massive scalars by the higher-dimensional Reissner-Nordstr\"{o}m black holes
Motivated by black hole experiments as a consequence of the TeV-scale gravity
arising from modern brane-world scenarios, we study the absorption problem for
the massive scalars when the spacetime background is a -dimensional
Reissner-Nordstr\"{o}m black hole. For analytic computation we adopt the
near-extreme condition in the spacetime background. It is shown that the
low-energy absorption cross section for the s-wave case holds an universality,
{\it i.e.} the absorption cross section equals to the area of the black hole
horizon divided by a velocity parameter.Comment: 11 pages, no figure, V2: version to appear in PL
Ratio of absorption cross section for Dirac fermion to that for scalar in the higher-dimensional black hole background
The ratio of the low-energy absorption cross section for Dirac fermion to
that for minimally coupled scalar is computed when the spacetimes are various
types of the higher-dimensional Reissner-Nordstr\"{o}m black holes. It is found
that the low-energy absorption cross sections for the Dirac fermion always goes
to zero in the extremal limit regardless of the detailed geometry of the
spacetime. The physical importance of our results is discussed in the context
of the brane-world scenarios and string theories.Comment: 12 pages, no figure, V2: several references added, version to appear
in PL
Heisenberg saturation of the Froissart bound from AdS-CFT
In a previous paper, we have analyzed high energy QCD from AdS-CFT and proved
the saturation of the Froissart bound (a purely QCD proof of which is still
lacking). In this paper we describe the calculation in more physical terms and
map it to QCD language. We find a remarkable agreement with the 1952 Heisenberg
description of the saturation (pre-QCD!) in terms of shockwave collisions of
pion field distributions. It provides a direct map between gauge theory physics
and the gravitational physics on the IR brane of the Randall-Sundrum model.
Saturation occurs through black hole production on the IR brane, which is in
QCD production of a nonlinear pion field soliton of a Born-Infeld action in the
hadron collision, that decays into free pions.Comment: 16 pages, 1 figure, latex, references added, typos correcte
Asymptotic Quasinormal Frequencies of Brane-Localized Black Hole
The asymptotic quasinormal frequencies of the brane-localized
-dimensional black hole are computed. Since the induced metric on the
brane is not an exact vacuum solution of the Einstein equation defined on the
brane, the real parts of the quasinormal frequencies do not approach
to the well-known value but approach to , where
is a number dependent on the extra dimensions. For the scalar perturbation
is reproduced when . For , however,
is smaller than . It is shown also that when ,
vanishes in the scalar perturbation. For the gravitational
perturbation it is shown that is reproduced when and . For different , however, is smaller
than . When , for example, approaches to
. Unlike the scalar perturbation
does not vanish regradless of the number of extra
dimensions.Comment: 15 pages, 1 eps figure: V2 one more reference added. The derivtaion
of the effective potential is explained in detail. Version of PL
Emissivities for the various Graviton Modes in the Background of the Higher-Dimensional Black Hole
The Hawking emissivities for the scalar-, vector-, and tensor-mode bulk
gravitons are computed in the full range of the graviton's energy by adopting
the analytic continuation numerically when the spacetime background is
-dimensional non-rotating black hole. The total emissivity for the
gravitons is only 5.16% of that for the spin-0 field when there is no extra
dimension. However, this ratio factor increases rapidly when the extra
dimensions exist. For example, this factor becomes 147.7%, 595.2% and 3496%
when the number of extra dimensions is 1, 2 and 6, respectively. This fact
indicates that the Hawking radiation for the graviton modes becomes more and
more significant and dominant with increasing the number of extra dimensions.Comment: 14 pages, 5 eps figures, V2: the incorrect multiplicities are
corrected. PLB versio
Condition for Superradiance in Higher-dimensional Rotating Black Holes
It is shown that the superradiance modes always exist in the radiation by the
-dimensional rotating black holes. Using a Bekenstein argument the
condition for the superradiance modes is shown to be
for the scalar, electromagnetic and gravitational waves when the spacetime
background has a single angular momentum parameter about an axis on the brane,
where is a rotational frequency of the black hole and is an
azimuthal quantum number of the radiated wave.Comment: 8 pages, no figure, v2: references added, version to appear in PL
Condition for the Superradiance Modes in Higher-Dimensional Rotating Black Holes with Multiple Angular Momentum Parameters
The condition for the existence of the superradiance modes is derived for the
incident scalar, electromagnetic and gravitational waves when the spacetime
background is a higher-dimensional rotating black hole with multiple angular
momentum parameters. The final expression of the condition is , where is an angular frequency of the black
hole and, and are the energy of the incident wave and the -th
azimuthal quantum number. The physical implication of this condition in the
context of the brane-world scenarios is discussed.Comment: 11 pages, no figur
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.
Higher dimensional inhomogeneous dust collapse and cosmic censorship
We investigate the occurrence and nature of a naked singularity in the
gravitational collapse of an inhomogeneous dust cloud described by higher
dimensional Tolman-Bondi space-times. The naked singularities are found to be
gravitationally strong in the sense of Tipler. Higher dimensions seem to favour
black holes rather than naked singularities.Comment: 15 pages, LaTeX, 1 figure, 2 table
High energy QCD scattering, the shape of gravity on an IR brane, and the Froissart bound
High-energy scattering in non-conformal gauge theories is investigated using
the AdS/CFT dual string/gravity theory. It is argued that strong-gravity
processes, such as black hole formation, play an important role in the dual
dynamics. Further information about this dynamics is found by performing a
linearized analysis of gravity for a mass near an infrared brane; this gives
the far field approximation to black hole or other strong-gravity effects, and
in particular allows us to estimate their shape. From this shape, one can infer
a total scattering cross-section that grows with center of mass energy as ln^2
E, saturating the Froissart bound.Comment: 27 pages, 1 fig, harvmac. v2: references added, typos corrected v3:
typo correcte
- …