Method of Green's functions in the theory of quantum kinetic equations. I

The solution of the dynamic equation is strongly degenerate for systems with an infinite number of degrees of freedom. A causality principle is stated, whereby the particular solution of the dynamic equation, which is at the same time a solution of the kinetic equation, can be selected. The principle is applied here to the multitime formalism of correlation functions. A basis is thus obtained for the method of Green's time-temperature functions in the theory of kinetic equations.The author thanks all those who have discussed the topics in this paper with him, particularly V. L. Bonch-Bruevich, D.A. Kirzhnits, V.M. Fain, E.S. Fradkin, and A. S. Shekhter.