Has NANOGrav found first evidence for cosmic strings?

TL;DR

This paper suggests that the recent NANOGrav data indicating a stochastic gravitational-wave background could be explained by cosmic strings, and shows that future experiments will explore the relevant parameter space.

Contribution

It provides a detailed interpretation of NANOGrav's findings as evidence for cosmic strings and analyzes the parameter space detectable by upcoming experiments.

Findings

NANOGrav's data can be explained by cosmic-string induced gravitational waves.

Future experiments will probe the entire viable cosmic-string parameter space.

Cosmic strings with certain tensions and loop sizes are consistent with observations.

Abstract

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has recently reported strong evidence for a stochastic common-spectrum process affecting the pulsar timing residuals in its 12.5-year data set. We demonstrate that this process admits an interpretation in terms of a stochastic gravitational-wave background emitted by a cosmic-string network in the early Universe. We study stable Nambu-Goto strings in dependence of their tension $G\mu$ and loop size $\alpha$ and show that the entire viable parameter space will be probed by an array of future experiments.