Electroweak bubble wall expansion: gravitational waves and baryogenesis
  in Standard Model-like thermal plasma
  Computing the properties of the bubble wall of a cosmological first order
phase transition at electroweak scale is of paramount importance for the
correct prediction of the baryon asymmetry of the universe and the spectrum of
gravitational waves. By means of the semi-classical formalism we calculate the
velocity and thickness of the wall using as theoretical framework the scalar
singlet extension of the SM with a parity symmetry and the SM effective field
theory supplemented by a dimension six operator. We use these solutions to
carefully predict the baryon asymmetry and the gravitational wave signals. The
singlet scenario can easily accommodate the observed asymmetry but these
solutions do not lead to observable effects at future gravity wave experiments.
In contrast the effective field theory fails at explaining the baryon abundance
due to the strict constraints from electric dipole moment experiments, however,
the strongest solutions we found fall within the sensitivity of the LISA
experiment. We provide a simple analytical approximation for the wall velocity
which only requires calculation of the strength and temperature of the
transition and works reasonably well in all models tested. We find that
generically the weak transitions where the fluid approximation can be used to
calculate the wall velocity and verify baryogenesis produce signals too weak to
be observed in future gravitational wave experiments. Thus, we infer that GW
signals produced by simple SM extensions visible in future experiments are
likely to only be produced in strong transitions described by detonations with
highly relativistic wall velocities.
