In this paper we compare different theoretical approaches to describe the
dispersion of collective modes in Yukawa fluids when the inter-particle
coupling is relatively weak, so that kinetic and potential contributions to the
dispersion relation compete. Thorough comparison with the results from
molecular dymamics simulation allows us to conclude that in the regime
investigated the best description is provided by the sum of the generalized
excess bulk modulus and the Bohm-Gross kinetic term.Comment: 9 pages, 7 figure