Vorticity, kinetic energy, and suppressed gravitational wave production
  in strong first order phase transitions
  We have performed the first 3-dimensional simulations of strong first-order
thermal phase transitions in the early Universe. For deflagrations, we find
that the rotational component of the fluid velocity increases as the transition
strength is increased. For detonations, however, the rotational velocity
component remains constant and small. We also find that the efficiency with
which kinetic energy is transferred to the fluid falls below theoretical
expectations as we increase the transition strength. The probable origin of the
kinetic energy deficit is the formation of reheated droplets of the metastable
phase during the collision, slowing the bubble walls. The rate of increase in
the gravitational wave energy density for deflagrations in strong transitions
is suppressed compared to that predicted in earlier work. This is largely
accounted for by the reduction in kinetic energy. Current modelling therefore
substantially overestimates the gravitational wave signal for strong
transitions with deflagrations, in the most extreme case by a factor of
$10^{3}$. Detonations are less affected.
