Bubble Wall Velocity in a First Order Electroweak Phase Transition

We calculate the velocity and thickness of a bubble wall at the electroweak phase transition in the minimal standard model. We model the wall with semiclassical equations of motion and show that friction arises from the deviation of massive particle populations from thermal equilibrium. We treat these with Boltzmann equations in a fluid approximation. Our technique allows us to account for particle transport, and to determine the wall thickness dynamically. We find that the wall is significantly thicker than at phase equilibrium, and that the velocity is fairly high, vw0.6c for mH0ex0ex=0ex0ex50 GeV.