Nuclear collective response calculated with realistic forces

We report upon calculations of a complete set of response functions for nuclear matter. The calculations are performed in the Tamm-Dancoff approximation using a reaction matrix calculated with a realistic interaction. (This interaction was obtained in the application of the one-boson-exchange model to the description of nucleon-nucleon scattering.) We stress the importance of performing such calculations with realistic interactions. We also indicate that a reasonable result for the response in the scalar-isoscalar channel can only be obtained using an effective interaction that saturates at the correct density for nuclear matter. Therefore, we calculate the reaction matrix in the scalar-isoscalar channel using the recently developed relativistic Brueckner-Hartree-Fock theory. (Relativistic effects are less important in other channels and are neglected in these calculations in all channels other than the scalar-isoscalar channel.) We find zero-sound modes in several channels for excitations of small momentum. We also study the evolution of the nuclear response for increasing values of the momentum, in the range 0<q/k/sub F/< or =1.0, or 0<q/k/sub F/< or =1.5 in some cases, and discuss the recent data on the ratio of the spin-dependent longitudinal to the transverse response for proton scattering on 208Pb