The Sound of Dark Sectors in Pulsar Timing Arrays

Abstract

A phase transition in the dark sector (DS) presents a promising explanation for the stochastic gravitational wave (GW) signals detected in recent observations by Pulsar Timing Arrays (PTAs). Instead of focusing solely on fitting data with phenomenological parameters, we systematically delineate simple, underlying dark sector (DS) models at the microscopic, Lagrangian level and uncover the conditions required to yield the GW spectrum observed by PTAs. We also illustrate the possibilities of the DS cosmology, which may include a dark matter candidate with a $\mathcal{O}$(MeV) mass.