Horizon spectroscopy in and beyond general relativity

In this work we generalize the results for the entropy spectra typically derived for black holes in general relativity to a generic horizon within the spherically symmetric (asymptotically flat and nonflat) space-times of more general theories of gravity. We use all the standard approaches-Bekenstein's universal lower bound on the entropy transition, the highly damped quasinormal modes and reduced phase-space quantization-to derive the spectra. In particular, the three approaches show that the Bekenstein-like spectra for the horizon entropy is a robust result. Our results confirm the suggestion made relatively recently by an independent fourth argument by Kothawala et al. [Phys. Rev. D 78, 104018 (2008)].