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

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.