Spherical and non-spherical bubbles in cosmological phase transitions
  The cosmological remnants of a first-order phase transition generally depend
on the perturbations that the walls of expanding bubbles originate in the
plasma. Several of the formation mechanisms occur when bubbles collide and lose
their spherical symmetry. However, spherical bubbles are often considered in
the literature, in particular for the calculation of gravitational waves. We
study the steady state motion of bubble walls for different bubble symmetries.
Using the bag equation of state, we discuss the propagation of phase transition
fronts as detonations and subsonic or supersonic deflagrations. We consider the
cases of spherical, cylindrical and planar walls, and compare the energy
transferred to bulk motions of the relativistic fluid. We find that the
different wall geometries give similar perturbations of the plasma. For the
case of planar walls, we obtain analytical expressions for the kinetic energy
in the bulk motions. As an application, we discuss the generation of
gravitational waves.
