Rolling Closed String Tachyons and the Big Crunch

TL;DR

This paper analyzes how closed string tachyons influence cosmological evolution, showing that tachyon-induced rolling leads to a universe crunch, with the dilaton evolving to strong coupling and the metric remaining fixed.

Contribution

It demonstrates that tachyon dynamics cause a finite-time universe crunch with fixed string metric and a dilaton rolling to strong coupling, extending understanding of string cosmology.

Findings

Tachyon-induced rolling results in a universe crunch in finite time.

The string metric remains fixed during the tachyon rolling process.

The dilaton evolves to strong coupling, influencing the cosmological outcome.

Abstract

We study the low-energy effective field equations that couple gravity, the dilaton, and the bulk closed string tachyon of bosonic closed string theory. We establish that whenever the tachyon induces the rolling process, the string metric remains fixed while the dilaton rolls to strong coupling. For negative definite potentials we show that this results in an Einstein metric that crunches the universe in finite time. This behavior is shown to be rather generic even if the potentials are not negative definite. The solutions are reminiscent of those in the collapse stage of a cyclic universe cosmology where scalar field potentials with negative energies play a central role.