NANOGrav results and Dark First Order Phase Transitions

Abstract

The recent NANOGrav evidence of a common-source stochastic background provides a hint to Gravitational Waves (GW) radiation from the Early Universe. We show that this result can be interpreted as a GW spectrum produced from First Order Phase Transitions (FOPTs) around a temperature in the KeV-MeV window. Such a class of FOPTs at temperatures much below the electroweak scale can be naturally envisaged in several Warm Dark Matter models such as Majoron Dark Matter.

More details and results on possible WDM-inspired GW spectra added, including more recent numerical tools in the subject. New references added. The main conclusions are substantially unchanged