A disintegrating cosmic string

TL;DR

This paper models a gravitational wave generated by the decay of a cosmic string, showing how the string's tension decreases and leaves behind an expanding Minkowski region.

Contribution

It introduces a simple Robinson-Trautman sandwich wave solution representing a decaying cosmic string and its associated gravitational wave.

Findings

The cosmic string's tension decreases through the wave.

The wave propagates into a Minkowski background with a wedge.

An expanding Minkowski region remains after the wave passes.

Abstract

We present a simple sandwich gravitational wave of the Robinson-Trautman family. This is interpreted as representing a shock wave with a spherical wavefront which propagates into a Minkowski background minus a wedge. (i.e. the background contains a cosmic string.) The deficit angle (the tension) of the string decreases through the gravitational wave, which then ceases. This leaves an expanding spherical region of Minkowski space behind it. The decay of the cosmic string over a finite interval of retarded time may be considered to generate the gravitational wave.