Observational prospects for gravitational waves from hidden or dark chiral phase transitions

We study the gravitational-wave (GW) signature of first-order chiral phase transitions (chi PTs) in strongly interacting hidden or dark sectors. We do so using several effective models in order to reliably capture the relevant nonperturbative dynamics. This approach allows us to explicitly calculate key quantities characterizing the chi PT without having to resort to rough estimates. Most importantly, we find that the transition's inverse duration beta normalized to the Hubble parameter H is at least 2 orders of magnitude larger than typically assumed in comparable scenarios, namely, beta/H greater than or similar to O(10(4)). The obtained GW spectra then suggest that signals from hidden chi PTs occurring at around 100 MeV might be in reach of LISA, while DECIGO and BBO may detect a stochastic GW background associated with transitions between roughly 1 GeV and 10 TeV. Signatures of transitions at higher temperatures are found to be outside the range of any currently proposed experiment. Even though predictions from different effective models are qualitatively similar, we find that they may vary considerably from a quantitative point of view, which highlights the need for true first-principle calculations such as lattice simulations