Retarded-Advanced N-point Green Functions in thermal field theories

Abstract

The general relationship between a Retarded-Advanced Green function of the Real Time formalism and analytical continuations of the Imaginary Time Amplitude is obtained via perturbation theory. A 4-point R-A function is, at most, a linear combination of three analytical continuations, and a 5-point R-A function of seven continuations. The R-A functions are written as the sum of one analytical continuation plus discontinuities across single momentum transfer variables. These discontinuities