Dark, Cold, and Noisy: Constraining Secluded Hidden Sectors with Gravitational Waves

Abstract

<p>We explore gravitational wave signals arising from first-order phase transitions occurring in a secluded hidden sector, allowing for the possibility that the hidden sector may have a different temperature than the Standard Model sector. Secluded hidden sectors are of particular interest for dark matter models at the MeV scale or below, which falls into the sensitivity range of pulsar timing arrays. Cosmological constraints on light degrees of freedom restrict the number of sub-MeV particles in a hidden sector, as well as the hidden sector temperature. Nevertheless, we find that observable first-order phase transitions can occur in two minimal benchmark models.</p>