Generalized enskog theory for homogeneous systems

We propose a generalization of the Enskog equation for homogeneous dense systems including the complete three-particle dynamics. To this end the time derivative of the one-particle distribution is represented in the thermodynamic limit as the sum of three terms describing the effect of the initials-particle correlations, collisions withins-particle clusters, and coupling ofs-particle clusters to the surrounding gaseous medium, respectively. The analysis of casess=2 ands=3 is performed both for hard spheres and for a smooth, repulsive interaction. On assuming the equilibrium structure and spatial dependence of terms reflecting the effect of the medium, we obtain fors=2 the Enskog equation, and fors=3 a new equation, going beyond the Enskog theory. Apart from the Enskog collision term it contains additional contributions, and can be shown to reduce to the Choh-Uhlenbeck equation in the long-time, low-density limit.