Effective pion-nucleon interaction in nuclear matter

Abstract

We discuss the modification of the interaction between a pion and a nucleon in the presence of an infinite medium of nucleons (nuclear matter). The theory presented here is covariant and is relevant to the calculation of the pion-nucleus optical potential. The specific effects considered are the modifications of the nucleon propagator due to the Pauli principle and the modification of the pion and nucleon propagators due to collisions with nucleons of the medium. We also discuss in detail the pion self-energy in the medium, paying close attention to off-shell effects. These latter effects are particularly important because of the rapid variation with energy of the fundamental pion-nucleon interaction. Numerical results are presented, the main feature being the appearance of a significant damping width for the (3, 3) resonance.