Some interesting violations of the Breitenlohner-Freedman bound

We demonstrate that AdS_5 x T^{pq} is unstable, in the sense of Breitenlohnerand Freedman, for unequal p and q. This settles, negatively, the long-standingquestion of whether the T^{pq} manifolds for unequal p and q might correspondto non-supersymmetric fixed points of the renormalization group. We also showthat the AdS_3 x S^7 vacuum of Sugimoto's USp(32) open string theory isunstable. This explains, at a heuristic level, the apparent absence of aheterotic string dual.Comment: 16 pages, latex. v2: minor correction