Sunday, August 4, 2013

1308.0018 (Caio F. B. Macedo et al.)

Absorption of planar massless scalar waves by Kerr black holes    [PDF]

Caio F. B. Macedo, Luiz C. S. Leite, Ednilton S. Oliveira, Sam R. Dolan, Luís C. B. Crispino
We consider planar massless scalar waves impinging upon a Kerr black hole, for general angles of incidence. We compute the absorption cross section via the partial wave approach, and present a gallery of results. In the low-frequency regime, we show that the cross section approaches the horizon area; in the high-frequency regime, we show that the cross section approaches the geodesic capture cross section. In the aligned case, we extend the complex angular momentum method to obtain a `sinc' approximation, which relates the regular high-frequency oscillations in the cross section to the properties of the polar null orbit. In the non-aligned case, we show, via a semi-analytic approximation, that the reduction in symmetry generates a richer, less regular absorption cross section. We separate the absorption cross section into corotating and counterrotating contributions, showing that the absorption is larger for counterrotating waves, as expected.
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