Quantization of Black Hole Entropy from Quasinormal Modes

In Phys. Rev. D 78 (2008) 104018 [arXiv:0807.1481], the conclusion that "entropy eigenvalues of GB black hole are discrete and equally spaced, but the area spacing is not equidistant" was firstly presented by Kothawala, Padmanabhan and Sarkar. In this paper, using the new physical interpretation of quasinormal modes proposed by Maggiore, we calculate the quantum spectra of entropy for various types of non-rotating black holes with no charge. The spectrum is obtained by imposing Bohr-Sommerfeld quantization condition to the adiabatic invariant quantity. We conjecture that the spacing of entropy spectrum is equidistant and is independent of the dimension of spacetime. However, the spacing of area spectrum depends on gravity theory. In Einstein's gravity, it is equally spaced, otherwise it is non-equidistant. This conjecture agrees with the result of Kothawala, Padmanabhan and Sarkar.