NUCLEON SELF-ENERGY IN THE RELATIVISTIC BRUECKNER APPROACH

The formalism of the relativistic (or Dirac-) Brueckner approach in in finite nuclear matter is described. For the nucleon-nucleon interactio n the one-boson exchange potentials Bonn A, B, C and for comparison th e Walecka model, are used. The T matrix is determined from the Thompso n equation and is projected onto five covariant amplitudes. By the res triction to positive energy states an ambiguity arises in the relativi stic Brueckner approach which is discussed here in terms of the pseudo scalar and the pseudovector projection. The influence of the coupling of the nucleon via the T matrix as an effective two-nucleon interactio n to the nuclear medium is expressed by the self-energy. In particular we investigate the scalar and vector components of the self-energy fo r the different one-boson exchange potentials and discuss their densit y and momentum dependence. We estimate the uncertainty of the self-ene rgy due to the pseudoscalar and the pseudovector choice. Usually the m omentum dependence of the self-energy is thought to be weak, however, we find that this depends on the one-boson exchange potentials. For th e Bonn potentials, in contrast to the aw potential, the momentum depen dence is strikingly strong above as well as below the Fermi surface. W e compare with the results of other groups and study the effects on th e equation of state and the nucleon optical potential.