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 ($\chi$PT) in strongly interacting hidden or dark sectors. We do so
using several effective models in order to reliably capture the relevant
non-perturbative 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 two orders of
magnitude larger than typically assumed in comparable scenarios, namely
$\beta/H\gtrsim\mathcal{O}(10^4)$. The obtained GW spectra then suggest that
signals from hidden $\chi$PTs occurring at around 100 MeV can 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.
