TWO-PERIOD GREEN'S FUNCTION IN STATISTICAL PHYSICS

Various aspects of the application of Green's functions in statistical physics are reviewed, and the future applications of two-period functions (retarding and advancing) are analyzed. The principle properties of the two- period Green's function and their simplest application in irreversible process theory, in the theory of superconductors, in ferromagnetics, and in electron- lattice reactions in common metals and semiconductors are discussed. It is also shown that the causal Green's functions can be successfully replaced with retarding and advancing Green's functions in the analytical expansion of the complex plane. Statistical mechanics sometimes employs the Motsubara temperature Green's functions which are not related to time; however, they are less adaptable than the temperature-time Green's functions. (R.V.J.)