Instability in near-horizon geometries of even-dimensional Myers-Perry black holes

We study the gravitational, electromagnetic and scalar field perturbations on the near-horizon geometries of the even-dimensional extremal Myers-Perry black holes. By dimensional reduction, the perturbation equations are reduced to effective equations of motion in AdS2. We find that some modes in the gravitational perturbations violate the Breitenlöhner-Freedman bound in AdS2. This result suggests that the even-dimensional (near-)extremal Myers-Perry black holes are unstable against gravitational perturbations. We also discuss implications of our results to the Kerr-CFT correspondence.