Kinetic equations for the phase—space-time correlation functions contain memory functions that involve projection operators. It is shown that these memory functions can be represented by integral equations involving only real-time correlation functions, thereby eliminating the projection operators completely in the kinetic description of correlation functions. The weak-coupling and density expansions of the memory functions have been obtained through these integral equations.

• Received 5 July 1972

DOI:https://doi.org/10.1103/PhysRevA.7.182