Chern-Simons diffusion rate near the electroweak phase transition for mH ≈ mW Original Research Article

The rate of B-violation in the standard model at finite temperature is closely related to the diffusion rate Γ of Chern-Simons number. We compute this rate for mH ≈ mW in the classical approximation in an effective SU(2)-Higgs model, using Krasnitzʹs algorithm. The parameters in the effective hamiltonian are determined by comparison with dimensional reduction. In the high temperature phase we find Γ/V(αWT)4 ≈ 1, neglecting a finite renormalization. In the low temperature phase near the transition we find the rate to be much larger than might be expected from previous analytic calculations based on the sphaleron.