Green's functions and admittances of nonequilibrium systems in a quasilinear approximation

On the basis of the non-linear response theory developed in [1], the Green functions and the kinetic coefficients of quasilinear approximation are considered. In this approximation the response of a system is calculated in the linear approximation with respect to the external force entering explicitly, but it depends functionally on the exact solutions of the integro-differential macroscopical balance equations, which tekes into account external forces as well as possible proper irreversible processes in non-equilibrium system. In the approximation used some general properties of non-equilibrium Green functions are considered as well as various forms of the perturbation theory with respect to internal interaction between subsystems.