Correlations and the relativistic structure of the nucleon self-energy

A key point of Dirac-Brueckner-Hartree-Fock calculations for nuclear matter is to decompose the self-energy of the nucleons into Lorentz scalar and vector components. A new method is introduced for this decomposition. It is based on the dependence of the single-particle energy on the small components in the Dirac spinors used to calculate the matrix elements of the underlying N N interaction. The resulting Dirac components of the self-energy depend on the momentum of the nucleons. At densities around and below the nuclear matter saturation density this momentum dependence is dominated by the non-locality of the Brueckner G matrix. At higher densities these correlation effects are suppressed and the momentum dependence due to the Fock exchange terms is getting more important. Differences between symmetric nuclear matter and neutron matter are discussed. Various versions of the Bonn potential are considered. (author)