Self-interacting dark matter implied by nano-Hertz gravitational waves

Understand

The self-interacting dark matter (SIDM) paradigm offers a potential solution to the small-scale structure problems faced by collision-less cold dark matter.

• This framework incorporates self-interactions among dark matter particles, typically mediated by a particle with a MeV-scale mass.
• Recent evidences of nano-Hertz gravitational waves from pulsar timing arrays (PTAs) such as NANOGrav, CPTA, EPTA, and PPTA suggest the occurrence of a first-order phase transition (FOPT) at a MeV-scale temperature.
• Considering the close proximity between these two scales, we propose that the mediator mass in the SIDM model originates from the spontaneous breaking of a $U(1)'$ symmetry, which is driven by the FOPT indicated by PTA data.