FINITE-TEMPERATURE RETARDED AND ADVANCED GREEN-FUNCTIONS

The relation is established between retarded/advanced (RA) Green functions and the "physical"/"ghost" ones of the standard real-time formalism of finite temperature field theory (RTFT) for arbitrary time-path parameter-sigma. Causal combinations of RTFT-Green functions are identified with specific RA-Green functions. It is argued that the imaginary part of the two-point RA-Green function is related to a physical reaction rate, and the real part of the three-point function to an effective coupling constant.