Strings in a Time-Dependent Orbifold

TL;DR

This paper investigates string theory in a time-dependent orbifold with a null singularity, analyzing quantization and scattering amplitudes to understand string behavior across a big crunch/big bang transition.

Contribution

It provides a detailed quantization of strings in a null singularity orbifold and examines scattering amplitudes near the singularity, suggesting strings may traverse the singularity.

Findings

Strings can pass through the singularity from contraction to expansion

Tree and one-loop amplitudes show interesting behavior near the singularity

Divergent scattering amplitudes indicate need for further study

Abstract

We consider string theory in a time dependent orbifold with a null singularity. The singularity separates a contracting universe from an expanding universe, thus constituting a big crunch followed by a big bang. We quantize the theory both in light-cone gauge and covariantly. We also compute some tree and one loop amplitudes which exhibit interesting behavior near the singularity. Our results are compatible with the possibility that strings can pass through the singularity from the contracting to the expanding universe, but they also indicate the need for further study of certain divergent scattering amplitudes.