Stringy instability of topologically non-trivial AdS black holes and of de Sitter S-brane spacetimes

Seiberg and Witten have discussed a specifically "stringy" kind of instability which arises in connection with "large" branes in asymptotically Ads spacetimes. It is easy to see that this instability actually arises in most five-dimensional asymptotically Ads black hole string spacetimes with non-trivial horizon topologies. We point out that this is a more serious problem than it may at first seem, for it cannot be resolved even by taking into account the effect of the branes on the geometry of spacetime. (It is ultimately due to the topology of spacetime, not its geometry.) Next, assuming the validity of some kind of dS/CFF correspondence, we argue that asymptotically de Sitter versions of the Hull-Strominger-Gutperle S-brane spacetimes are also unstable in this "topological" sense, at least in the case where the R-symmetries are preserved. We conjecture that this is due to the unrestrained creation of "late" branes, the spacelike analogue of large branes, at very late cosmological times. (C) 2003 Elsevier Science B.V. All rights reserved.