Off-shell behavior of the in-medium nucleon-nucleon cross section

The properties of nucleon-nucleon scattering inside dense nuclear matter are investigated. We use the relativistic Brueckner-Hartree-Fock model to determine on-shell and half off-shell in-medium transition amplitudes and cross sections. At finite densities the on-shell cross sections are generally suppressed. This reduction is, however, less pronounced than found in previous works. In case the outgoing momenta are allowed to be off energy shell the amplitudes show a strong variation with momentum. This description allows one to determine in-medium cross sections beyond the quasiparticle approximation, accounting thereby for the finite width which nucleons acquire in the dense nuclear medium. For reasonable choices of the in-medium nuclear spectral width, i.e., Γ≤40 MeV, the resulting total cross sections are, however, reduced by not more than about 25% compared to the on-shell values. Off-shell effects are generally more pronounced at large nuclear matter densities.