Multiple-point and multiple-time correlation functions in a hard-sphere fluid.

A recent mode-coupling theory of higher-order correlation functions is tested on a simple hard-sphere fluid system at intermediate densities. Multiple-point and multiple-time correlation functions of the densities of conserved variables are calculated in the hydrodynamic limit and compared to results obtained from event-based molecular dynamics simulations. It is demonstrated that the mode-coupling theory results are in excellent agreement with the simulation results provided that dissipative couplings are included in the vertices appearing in the theory. In contrast, simplified mode-coupling theories in which the densities obey Gaussian statistics neglect important contributions to both the multiple point and multiple-time correlation functions on all time scales.