Spectroscopy of the rotating BTZ black hole via adiabatic invariance
  According to Bohr-Sommerfeld quantization rule, an equally spaced horizon area spectrum of a static, spherically symmetric black hole was obtained under an adiabatic invariant action. This method can be extended to the rotating black holes. As an example, we apply this method to the rotating BTZ black hole and obtain the quantized spectrum of the horizon area. It is shown that the area spectrum of the rotating BTZ black hole is equally spaced and irrelevant to the rotating parameter, which is consistent with the Bekenstein conjecture. Specifically, the derivation do not need the quasinormal frequencies and the small angular momentum limit. 
Xian-Ming Liu, Xiao-Xiong Zeng, Wen-Biao Liu
gr-qc