On Time-dependent Backgrounds in Supergravity and String Theory

TL;DR

This paper explores various time-dependent backgrounds in supergravity and string theory, including de Sitter deformations, analytical continuations, and solvable models, revealing insights into cosmological singularities and symmetry restoration.

Contribution

It introduces new time-dependent solutions in supergravity and string theory, connecting gauge/gravity dualities, analytical continuations, and worldsheet models to cosmological phenomena.

Findings

Hubble parameter can restore chiral symmetry in confining gauge theories.

Some solutions describe a universe with a bounce between big bang and big crunch.

String propagation near Milne-type singularities may be non-singular.

Abstract

Time-dependent solutions of supergravity and string theory are studied. The examples are obtained from de Sitter deformation of gauge/gravity dualities, analytical continuation of static solutions, and ``exactly solvable'' worldsheet models. Among other things, it is shown that turning on a Hubble parameter in the background of a confining gauge theory in four dimensions can restore chiral symmetry. Some of the solutions obtained from analytical continuation have the interpretation of a universe with a bounce separating a big bang from a big crunch singularity. In the worldsheet context, it is argued why string propagation close to a Milne-type cosmological singularity might be physically non-singular.