We investigate the absorption of a massive and charged scalar field in a Reissner-Nordstr\"om background. We compare our numerical results for the absorption cross section, obtained for arbitrary frequencies, with the low- and high-frequency limits. We find, in particular, that the total absorption cross section can be negative, showing that planar scalar waves can be superradiantly amplified by black holes.
@article{arxiv.1511.02634,
title = {Superradiance in static black hole spacetimes},
author = {Carolina L. Benone and Luís C. B. Crispino},
journal= {arXiv preprint arXiv:1511.02634},
year = {2016}
}