Time-dependent triplet correlation functions and pressure derivative of the dynamic structure factor

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Abstract
Correlation functions at two times and three space points are considered as an extension of recent investigations of time-independent triplet correlation functions. The formal kinetic theory for these functions is shown to be the same as that for the usual two-point functions. The results are expressed in terms of the solution to the formal one-particle kinetic equation, a two-particle functional that is the kernel for the collision operator in the one-particle equation, and various equilibrium static correlation functions. In particular, the three-point density correlation function is considered and related to the pressure derivative of the dynamic structure factor as a means to indicate indirect experimental accessibility to the triplet functions. A simple but relatively accurate kinetic model for the dynamic structure factor is used to illustrate the behavior of the pressure derivative.