Anisotropies in the gravitational wave background as a probe of the cosmic string network

TL;DR

This paper investigates how anisotropies in the gravitational wave background, caused by cosmic string cusps, can reveal properties of cosmic strings and constrain their parameters through pulsar timing array observations.

Contribution

It provides estimates of GW background anisotropies from cosmic string cusps and shows how these anisotropies can constrain string properties like initial loop size.

Findings

Anisotropy levels depend strongly on initial loop size α.

Measuring anisotropies can constrain cosmic string parameters.

Shifting GW observation frequency probes different parameter regions.

Abstract

Pulsar timing arrays are one of the powerful tools to test the existence of cosmic strings through searching for the gravitational wave background. The amplitude of the background connects to information on cosmic strings such as the tension and string network properties. In addition, one may be able to extract more information on properties of cosmic strings by measuring anisotropies in the gravitational wave (GW) background. In this paper, we provide estimates of the level of anisotropy expected in the GW background generated by cusps on cosmic strings. We find that the anisotropy level strongly depends on the initial loop size $\alpha$, and thus we may be able to put constraint on $\alpha$ by measuring the anisotropy of the GW background. We also find that certain regions of the parameter space can be probed by shifting the observation frequency of GWs.