Discontinuities and collision of gravitational waves in string theory

TL;DR

This paper investigates the nature of discontinuities and collisions of gravitational waves within string theory, revealing that null surfaces permit shock and impulsive waves, and analyzing their effects in specific models.

Contribution

It demonstrates that discontinuities in string theory are confined to null surfaces and explores their implications in colliding gravitational wave scenarios and WZW models.

Findings

Discontinuities must be on null surfaces.

Shock and impulsive waves are both possible.

Singularities can result from wave focusing in models.

Abstract

We examine here discontinuities in the metric, the antisymmetric tensor and the dilaton field which are allowed by conformal invariance. We find that the surfaces of discontinuity must necessarily be null surfaces and shock and impulsive waves are both allowed. We employ our results for the case of colliding plane gravitational waves and we discuss the SL(2,R)XSU(2)/RXR WZW model in the present prespective. In particular, the singularities encountered in this model may be viewed as the result of the mutual focusing of the colliding waves.