Backflow, retardation and relativistic effects on the longitudinal response function of nuclear matter

The relativistic RPA response function for quasielastic electron scattering in the sigma-ω model is analyzed in detail. The following three effects on the longitudinal response function are examined numerically, and analytically in the relativistic Landau theory; i) the backflow effect due to the longitudinal component of the ω-meson exchange between particle-hole states, ii) the relativistic effect from the difference between the Lorentz scalar and baryon densities, and iii) the retardation effect of the particle-hole interactions. The first two effects, which are neglected in nonrelativistic models, play an important role in the longitudinal response function. (orig.)