Problems of Perturbation Series in Non-Equilibrium Quantum Field Theories

Abstract

In the standard framework of non-equilibrium quantum field theories, the pinch singularities associated to multiple products of $\delta$-functions do not cancel in a perturbative expansion unless the particle distributions are those for a system in thermal and chemical equilibrium.

Comments: 10 pages, 2 figures, Cern preprint CERN-TH.7271/94