Time-dependent self-diffusion coefficient of interacting Brownian particles

We study the time-dependent self-diffusion coefficient for a suspension of interacting, spherical Brownian particles. Guided by an exact result for a dilute suspension of hard spheres, we conjecture that the Fourier transform of the memory function may be represented as a meromorphic function of the square root of the frequency. We show that a two-pole approximation provides a suitable framework for the analysis of experimental data.