Gravitational waves from metastable cosmic strings in Pati-Salam model in light of new pulsar timing array data

Abstract

A series of pulsar timing arrays (PTAs) recently observed gravitational waves at the nanohertz frequencies. Motivated by this remarkable result, we present a novel class of Pati-Salam models that give rise to a network of metastable cosmic strings, offering a plausible explanation for the observed PTA data. Besides, we introduce a hybrid inflationary scenario to eliminate magnetic monopoles that arise during the spontaneous symmetry breaking of the Pati-Salam gauge group to the Standard Model. The resulting scalar spectral index is compatible with Planck data, and the tensor-to-scalar ratio is anticipated to be extremely small. Moreover, we incorporate a non-thermal leptogenesis to generate the required baryon asymmetry in our framework. Finally, the gravitational wave spectra generated by the metastable cosmic strings not only correspond to signals observed in recent PTAs, including NANOGrav, but are also within the exploration capacity of both present and future ground-based and space-based experiments.