We consider scalar field perturbations about asymptotically Lifshitz black holes with dynamical exponent z in D dimensions. We show that, for suitable boundary conditions, these Lifshitz black holes are stable under scalar field perturbations. For z=2, we explicitly compute the quasinormal mode frecuencies, which result to be purely imaginary, and then obtain the damping-off of the scalar field perturbation in these backgrounds. The general analysis includes, in particular, the z=3 black hole solution of three-dimensional massive gravity.
A recent paper [arXiv:0801.4566] claims that topologically massive gravity contains only chiral boundary excitations at a particular value of the Chern-Simons coupling. On the other hand, propagating bulk degrees of freedom were found even at the chiral point in [arXiv:0803.3998]. The two references use very different methods, making comparison of their respective claims difficult. In this letter, we use the method of [arXiv:0801.4566] to construct a tower of propagating bulk states satisfying standard AdS boundary conditions. Our states have finite norm, with sign opposite to that of right-moving boundary excitations. Our results thus agree with [arXiv:0803.3998] and disagree with [arXiv:0801.4566].
