Some interesting violations of the Breitenlohner-Freedman bound

We demonstrate that AdS5 × T pq is unstable, in the sense of Breitenlohner and Freedman, for unequal p and q. This settles, negatively, the long-standing question of whether the T pq manifolds for unequal p and q might correspond to non-supersymmetric fixed points of the renormalization group. We also show that the AdS3×S vacuum of Sugimoto’s USp(32) open string theory is unstable. This explains, at a heuristic level, the apparent absence of a heterotic string dual.