Schwarzschild-like black holes: Light-like trajectories and massless scalar absorption

Black holes are among the most intriguing objects in nature. They are believed to be fully described by General Relativity (GR), and the astrophysical black holes are expected to belong to the Kerr family, obeying the no-hair theorems. Alternative theories of gravity or parameterized deviations of GR allow black hole solutions, which have additional parameters other than mass and angular momentum. We analyze a Schwarzschild-like metric, proposed by Johannsen and Psaltis, characterized by its mass and a deformation parameter. We compute the absorption cross section of massless scalar waves for different values of this deformation parameter and compare it with the corresponding scalar absorption cross section of the Schwarzschild black hole. We also present analytical approximations for the absorption cross section in the high-frequency regime. We check the consistence of our results comparing the numerical and analytical approaches, finding excellent agreement.Comment: 8 pages, 14 figure

The B's

That was a good time for movies and even a better time for outrageous stories about the movies. There was this starlet who attributed the loss of her virginity to horseback riding. There was another one who swore that she only spoke Tagalog to the maids. A director wanted an actress in his film to get an acting trophy so badly it took him three days to shoot a rape scene and added two more rapists without informing his actress, making her screams sound really shrill. In our town, the most famous tale about a movie theater during that time was about a woman who hid a grenade inside her beehive. How the guard or any of the staff discovered it was never known. Nobody can confirm what day or what hour it happened. What remained were the hairdo and the weapon. These were two details that were enough to scare some parents to forbid their children from going to the movies with the added pacifying explanation that “these movies are eventually going to be shown on TV anyway.

Low-frequency absorption cross section of the electromagnetic waves for the extreme Reissner-Nordstrom black holes in higher dimensions

We investigate the low-frequency absorption cross section of the electromagnetic waves for the extreme Reissner-Nordstrom black holes in higher dimensions. We first construct the exact solutions to the relevant wave equations in the zero-frequency limit. In most cases it is possible to use these solutions to find the transmission coefficients of partial waves in the low-frequency limit. We use these transmission coefficients to calculate the low-frequency absorption cross section in five and six spacetime dimensions. We find that this cross section is dominated by the modes with l=2 in the spherical-harmonic expansion rather than those with l=1, as might have been expected, because of the mixing between the electromagnetic and gravitational waves. We also find an upper limit for the low-frequency absorption cross section in dimensions higher than six.Comment: 7 pages, 1 figure, Phys. Rev. D (to appear

The Unruh effect and its applications

It has been thirty years since the discovery of the Unruh effect. It has played a crucial role in our understanding that the particle content of a field theory is observer dependent. This effect is important in its own right and as a way to understand the phenomenon of particle emission from black holes and cosmological horizons. Here, we review the Unruh effect with particular emphasis to its applications. We also comment on a number of recent developments and discuss some controversies. Effort is also made to clarify what seems to be common misconceptions.Comment: 53 pages, 11 figures, submitted to Reviews of Modern Physic