A note on the singularity theorem for supergravity SD-branes

Abstract

Recently, a singularity theorem for full SD-brane spacetimes was given in hep-th/0305055. We comment on the relation between this and previous work as well as provide a more geometric formulation interpreted as a no-go theorem. We then point out that some setups of physical interest escape the theorem: cosmological applications, half-SDp-branes and decaying unstable Dp-branes for general p. We also provide indications that the space-filling full SD8-brane (in d=10) escapes as well, because of the important role of Ramond-Ramond fields. In any case, tachyon cosmology is not ruled out by the no-go theorem. Lastly, we remark upon interesting directions for potential generalizations of the theorem, and quantum corrections.