Rotational correlations in rough sphere fluids

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Abstract
The coupling of the angular velocity of a test rough sphere to the collective modes of the surrounding bath of rough spheres is studied as a function of the mass and diameter of the test sphere using renormalized kinetic theory. As the diameter of the tagged particle increases, the collective contribution to the relaxation changes from a situation where coupling to the fluid transverse angular velocity field dominates to one in which coupling to the transverse linear velocity field dominates. As the mass of the test particle increases, the collective contribution becomes increasingly sensitive to the nonhydrodynamic states which appear in the kinetic theory. The long time behavior of the angular velocity correlation function and the associated memory kernels are found to have interesting dependence on the test sphere diameter. The results are used to elucidate some features of the hydrodynamic character of microscopic relaxation processes.