Does the Tachyon Matter?

TL;DR

This paper investigates time-dependent solutions in Einstein-Maxwell gravity coupled with tachyon matter, revealing singularities and analyzing tachyon behavior as a probe, contributing to understanding unstable D-brane decay in string theory.

Contribution

It presents new time-dependent solutions with S-brane charge in Einstein-Maxwell-tachyon systems and studies tachyon backreaction and singularities.

Findings

Tachyon solutions resemble space-like branes and do not break Lorentzian R-symmetry.

Tachyon energy density diverges at intermediate times, causing a space-like singularity.

Tachyon exhibits constant energy density at early and late times with vanishing pressure.

Abstract

We study time-dependent solutions of Einstein-Maxwell gravity in four dimensions coupled to tachyon matter--the Dirac-Born-Infeld Lagrangian that provides an effective description of a decaying tachyon on an unstable D-brane in string theory. Asymptotically, the solutions are similar to the recently studied space-like brane solutions and carry S-brane charge. They do not break the Lorentzian R-symmetry. We study the tachyon matter as a probe in such a background and analyze its backreaction. For early/late times, the tachyon field has a constant energy density and vanishing pressure as in flat space. On the other hand, at intermediate times, the energy density of the tachyon diverges and produces a space-like curvature singularity.