Bubble wall velocity in a first order electroweak phase transition.

Lancaster UniversitySchool of Physics and ChemistryLancaster LA1 4YB, UKABSTRACTWe calculate the velocity and thickness of a bubble wall at the electroweak phasetransition in the Minimal Standard Model. We model the wall with semiclassicalequations ofmotionandshow thatfrictionarisesfromthedeviation ofmassive particlepopulations from thermal equilibrium. We treat these with Boltzmann equationsin a fluid approximation in the background of the wall. Our analysis improves onthe previous work by using the two loop effective potential, accounting for particletransport, and determining the wall thickness dynamically. We find that the wall issignificantly thicker than at phase equilibrium, and that the velocity is fairly high,v