A hidden self-interacting dark matter sector with first order cosmological phase transition and gravitational wave

A dark scalar mediator can easily realize the self-interacting dark matter scenario and satisfy the constraint of the relic density of the dark matter. When the hidden sector is highly decoupled from the visible sector, the gravitational waves produced by the first order phase transition resulted from this dark scalar mediator will be an important signature to probe the dark sector physics. The simplest dark sector with one scalar and one Dirac fermion is studied in this work. A generic quartic finite-temperature potential is used to induce the strong first order phase transition. A joint analysis of the self-interacting dark matter, the relic density of the dark matter and the first order phase transition shows that the mass range of the dark scalar is about $(4\times 10^{-4} \sim 3)~\rm GeV$. For the dark matter, when the temperature ratio $\xi$ between the hidden sector and the visible sector is larger than 0.1, its mass range is about $(10~ \rm MeV\sim 10~ \rm GeV)$. The produced gravitational waves have a peak frequency of $(10^{-6}\sim 10^{-3}) ~\rm Hz$ for a temperature ratio $0.1<\xi<1$, which may be detectable in future measurements.