Has NANOGrav found first evidence for cosmic strings?

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.

Comments: 7 pages, 3 figures. v2: revised treatment of the higher cosmic-string modes [see Eq. (6)], resulting in a few numerical but no qualitative changes. v3: matches version published in PRL