Gravitational waves and electroweak baryogenesis in a global study of
  the extended scalar singlet model
  We perform a global fit of the extended scalar singlet model with a fermionic
dark matter (DM) candidate. Using the most up-to-date results from the
$\mathit{Planck}$ measured DM relic density, direct detection limits from the
XENON1T (2018) experiment, electroweak precision observables and Higgs searches
at colliders, we constrain the 7-dimensional model parameter space. We also
find regions in the model parameter space where a successful electroweak
baryogenesis (EWBG) can be viable. This allows us to compute the gravitational
wave (GW) signals arising from the phase transition, and discuss the potential
discovery prospects of the model at current and future GW experiments. Our
global fit places a strong upper $\mathit{and}$ lower limit on the second
scalar mass, the fermion DM mass and the scalar-fermion DM coupling. In
agreement with previous studies, we find that our model can simultaneously
yield a strong first-order phase transition and saturate the observed DM
abundance. More importantly, the GW spectra of viable points can often be
within reach of future GW experiments such as LISA, DECIGO and BBO.
