Comments on Supergravity Description of S-branes

TL;DR

This paper critically examines supergravity models of S-branes, demonstrating that under certain symmetries, solutions are always singular, challenging recent claims and discussing the gravitational description of D-brane decay.

Contribution

It provides a no-go result showing that symmetric supergravity solutions for S-branes are inherently singular, countering previous assertions in the literature.

Findings

Most symmetric solutions are singular for p ≤ 7

Invalidates recent claims of non-singular solutions

Discusses limitations of gravitational descriptions of D-brane decay

Abstract

This is a note on the coupled supergravity-tachyon matter system, which has been earlier proposed as a candidate for the effective space-time description of S-branes. In particular, we study an ansatz with the maximal ISO(p+1)xSO(8-p,1) symmetry, for general brane dimensionality p and homogeneous brane distribution in transverse space \rho_\perp. A simple application of singularity theorems shows that (for p \le 7) the most general solution with these symmetries is always singular. (This invalidates a recent claim in the literature.) We include a few general comments about the possibility of describing the decay of unstable D-branes in purely gravitational terms.