Real-time dynamics with fermions on a lattice

The 1 + 1-dimensional abelian Higgs model with fermions is a toy model for the theory of electroweak baryogenesis. We study the dynamics of the model with axially coupled fermions in real-time. The model is defined on a space -time lattice to preserve gauge invariance and to obtain numerical stabilit y in a simple way. We take into account the phenomenon of lattice fermion d oubling. The dynamics is approximated by treating the inhomogeneous Bose fi elds classically, which is justified in a large N-f approximation. The back reaction on the Bose fields due to fermion field fluctuations is calculate d using a mode function expansion. We discuss and present numerical results for the response of fermions to sphaleron transitions, the renormalizabili ty of the effective equations of motion and non-perturbative dynamics in th e framework of non-equilibrium quantum field theory. The long-time behaviou r of the system is discussed and we speculate about applications to finite density calculations. (C) 1999 Elsevier Science B.V. All rights reserved.