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 $(4+n)$-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 $(4+n)$-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 $\omega$ do not approach to the well-known value $T_H \ln 3$ but approach to $T_H \ln k_n$, where $k_n$ is a number dependent on the extra dimensions. For the scalar perturbation $Re(\omega / T_H) = \ln 3$ is reproduced when $n = 0$. For $n \neq 0$, however, $Re(\omega / T_H)$ is smaller than $\ln 3$. It is shown also that when $n > 4$, $Im(\omega / T_H)$ vanishes in the scalar perturbation. For the gravitational perturbation it is shown that $Re(\omega / T_H) = \ln 3$ is reproduced when $n = 0$ and $n = 4$. For different $n$, however, $Re(\omega / T_H)$ is smaller than $\ln 3$. When $n = \infty$, for example, $Re(\omega / T_H)$ approaches to $\ln (1 + 2 \cos \sqrt{5} \pi) \approx 0.906$. Unlike the scalar perturbation $Im(\omega / T_H)$ 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 $(4+n)$-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 $(4+n)$-dimensional rotating black holes. Using a Bekenstein argument the condition for the superradiance modes is shown to be $0 < \omega < m \Omega$ for the scalar, electromagnetic and gravitational waves when the spacetime background has a single angular momentum parameter about an axis on the brane, where $\Omega$ is a rotational frequency of the black hole and $m$ 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 $0 < \omega < \sum_i m_i \Omega_i$, where $\Omega_i$ is an angular frequency of the black hole and, $\omega$ and $m_i$ are the energy of the incident wave and the $i$-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