Gravitational Wave Bursts from Cosmic String Cusps and Pseudocusps

TL;DR

This paper analyzes the gravitational wave bursts from cosmic string cusps and pseudocusps, revealing that non-relativistic points significantly contribute to emissions, increasing the expected burst rate.

Contribution

It provides a detailed numerical and analytical study of gravitational wave emissions from near-relativistic points on cosmic strings, expanding understanding beyond idealized cusps.

Findings

Gravitational wave emission follows a logarithmic decrease near relativistic points.

Non-relativistic points (up to 10^{-3} from c=1) contribute similarly to cusps.

Emission from these points can increase the effective number of cusps by about 1000 times.

Abstract

We study the relative contribution of cusps and pseudocusps, on cosmic (super)strings, to the emitted bursts of gravitational waves. The gravitational wave emission in the vicinity of highly relativistic points on the string follows, for a high enough frequency, a logarithmic decrease. The slope has been analytically found to be $^{-4}/_3$ for points reaching exactly the speed of light in the limit $c=1$. We investigate the variations of this high frequency behaviour with respect to the velocity of the points considered, for strings formed through a numerical simulation, and we then compute numerically the gravitational waves emitted. We find that for string points moving with velocities as far as $10^{-3}$ from the theoretical (relativistic) limit $c=1$, gravitational wave emission follows a behaviour consistent with that of cusps, effectively increasing the number of cusps on a string. Indeed, depending on the velocity threshold chosen for such behaviour, we show the emitting part of the string worldsheet is enhanced by a factor ${\cal O}(10^3)$ with respect to the emission of cusps only.