Soft contributions to the thermal Higgs width across an electroweak phase transition

Abstract

We estimate the equilibration rate of a nearly homogeneous Higgs field, displaced from its ground state during the onset of an electroweak phase transition. The computation is carried out with Hard Thermal Loop resummed perturbation theory, and a significant part of the result originates from Bose-enhanced $t$-channel $2\leftrightarrow 2$ scatterings. The expression is shown to be IR finite and gauge independent. Possible applications to Langevin simulations of bubble nucleation are mentioned, and we also contrast with the friction affecting bubble growth.