Quasinormal modes for topologically massive black hole

We calculate quasinormal modes of a massive scalar perturbation on the topologically massive black hole (CS-BTZ black hole). The chiral point of $\mu \ell=1$ corresponds to a newly extremal black hole. We show that there is no quasinormal modes at this point. Accordingly, we prove the unitarity of the CS-BTZ black hole at the chiral point.