Effective theory for real-time dynamics in hot gauge theories

For a high temperature non-Abelian plasma, we reformulate the hard thermal loop approximation as an effective classical thermal field theory for the soft modes. The effective theory is written in local Hamiltonian form, and the thermal partition function is explicitly constructed. It involves an ultraviolet cutoff which separates between hard and soft degrees of freedom in a gauge-invariant way, together with counterterms which cancel the cutoff dependence in the soft correlation functions. The effective theory is well suited for numerical studies of the non-perturbative dynamics in real time, in particular, for the computation of the baryon number violation rate at high temperature. (C) 1998 Elsevier Science B.V. All rights reserved.