Abstract
The North American Nanohertz Observatory for Gravitational Waves 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 Gμ and loop size α and show that the entire viable parameter space will be probed by an array of future experiments.
Highlights
Introduction.—Many models of new physics beyond the Standard Model predict cosmological phase transitions in the early Universe that lead to the spontaneous breaking of an Abelian symmetry [1]
An exciting phenomenological consequence of such phase transitions is the generation of a network of cosmic strings [2,3], vortexlike topological defects that restore the broken symmetry at their core [4]
In this Letter, we shall investigate the latter possibility, a cosmic-string-induced gravitational waves (GWs) signal at nanohertz frequencies, in light of the recent results reported by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) pulsar timing array (PTA) experiment [13,14]
Summary
The North American Nanohertz Observatory for Gravitational Waves 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 gravitationalwave background emitted by a cosmic-string network in the early Universe. If interpreted in terms of GWs, the NANOGrav signal indicates a GW amplitude at nanohertz frequencies that exceeds previous upper bounds This is remarkable and can be traced back to several factors, the most important of which being the choice of a uniform Bayesian prior on the amplitude of pulsar-intrinsic red-noise processes, which shifted signal power to red-noise power in previous PTA analyses [19]. The new NANOGrav results reinvigorate SGWB scenarios that had previously been believed to be severely constrained by PTA bounds
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