Perturbation theory for classical random processes with arbitrary preparation

Abstract

The perturbation theory for classical processes developed by Martin, Siggia, and Rose is clarified and extended so that it applies to systems prepared in arbitrary initial states and driven by arbitrary random forces. The necessary modifications are achieved by introducing additional bare vertices. The range of validity of the original scheme (including slight modifications) is discussed. Finally, a short comparison with other approaches to perturbation theory is given.