The Sphaleron Rate: Where We Stand

Abstract

I review what we know about the ``sphaleron rate'', which is the efficiency of baryon number violation at high temperatures of order 100 GeV in the Standard Model. The leading behavior at weak coupling in the symmetric phase is known accurately; Gamma = (10.7 +- .7) (g^2 T^2 / m_D^2) log(m_D/g^2T)α_w^5 T^4. At realistic values of the coupling our accuracy is worse. We also now have the tools to determine the rate nonperturbatively in the broken electroweak phase; the sphaleron rate there is slower than perturbative estimates.