Generalized transport equations in the theory of irreversible processes

Zubarev's nonequilibrium statistical operator method [1, 2] is used to study transport phenomena in a nonequilibrtum system. For the transport coefficients that depend on the frequency and wave vector, exact expressions of two types are obtained, these generalizing the Kubo formulas: in terms of a combination of time correlation functions and in terms of functions in which the evolution in time includes a certain projection operation. As an example, the hydrodynamics of a simple liquid is considered and the structure of density–density correlation functions is discussed.