SD-brane gravity fields and rolling tachyons

TL;DR

This paper develops a numerical model coupling open-string tachyon modes with bulk closed-string fields to resolve spacelike singularities in SD-brane gravity solutions, showing nonsingular, time-dependent evolution.

Contribution

It introduces a self-consistent numerical approach including backreaction and RR fields, demonstrating nonsingular SD-brane evolution and addressing prior singularity issues.

Findings

Solutions are asymptotically flat and time-reversal asymmetric.

The inclusion of backreaction resolves spacelike singularities.

Dilaton and curvature remain well-behaved for all time.

Abstract

S(pacelike)D-branes are objects arising naturally in string theory when Dirichlet boundary conditions are imposed on the time direction. SD-brane physics is inherently time-dependent. Previous investigations of gravity fields of SD-branes have yielded undesirable naked spacelike singularities. We set up the problem of coupling the most relevant open-string tachyonic mode to massless closed-string modes in the bulk, with backreaction and Ramond-Ramond fields included. We find solutions numerically in a self-consistent approximation; our solutions are naturally asymptotically flat and time-reversal asymmetric. We find completely nonsingular evolution; in particular, the dilaton and curvature are well-behaved for all time. The essential mechanism for spacetime singularity resolution is the inclusion of full backreaction between the bulk fields and the rolling tachyon. Our analysis is not the final word on the story, because we have to make some significant approximations, most notably homogeneity of the tachyon on the unstable branes. Nonetheless, we provide significant progress in plugging a gaping hole in prior understanding of the gravity fields of SD-branes.