Bubble Nucleation and Propagation at Electroweak Phase Transition.

The nucleation and propagation of bubbles of the broken symmetry phase of matter at the electroweak phase transition are investigated. It is shown that the bubble wall is mainly slowed by interactions with low momentum gauge boson pairs. The width of the bubble wall is significantly larger than the typical wavelength of particles which are reflected from it, which allows us to use a WKB approximation for the particle scattering. The width is also larger than the mean free path for these particles, which means that the gauge boson fluid remains close to local thermal equilibrium. This situation results in mildly relativistic motion of the bubble wall. As a result, the baryon number excess produced on the bubble wall is not much diluted by subsequent diffusion. We compute the effective equation of motion for the Higgs field, the approximate shape and the velocity of the bubble wall. We find gamma upsilon~1. We also study the hydrodynamic stability of the burning and find that the shape of the bubble wall is stable under hydrodynamic perturbation.