MG14 - Talk detail

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Abstract

The study of the massless-scalar-field greybody factors of rotating cohomogeneity-1 black holes is presented. The analysis is split in three cases: when the cosmological constant is zero, negative (dS), or positive (AdS). In cohomogeneity-1 class of spacetimes, the metric depends on a single coordinate. In this case, the angular part of the solution for the massless scalar field is analytically known. The equation for the radial part of the wave can be solved analytically in the low-frequency limit as well as in the asymptotic regions. Using the matched asymptotic expansion method, low-frequency greybody factors are obtained for the s-wave. However, in order to probe the superradiant regime, a numerical analysis is required. For asymptotically flat spacetimes, low-frequency limit greybody factors result in an absorption cross section that equals the black-hole horizon area. Independently of the cosmological constant value, the maximum amplification obtained decreases with the increase of the number of dimensions. In the case of dS black holes, the wave amplification gets enhanced with the increase of the absolute value of the cosmological constant. In the case of small AdS black holes, the greybody factors are characterized by peaks located very close to the normal frequencies of the pure AdS spacetime. Such peaks wane as the cosmological constant value increases. Also, because of these peaks, the maximum amplification observed in AdS black holes can be considerably larger than the one observed in spacetimes with vanishing cosmological constant. Comparisons between analytic and numerical results reveal excellent agreement.

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