RELATIVISTIC BRUECKNER-HARTREE-FOCK CALCULATIONS, WITH EXPLICIT INTERMEDIATE NEGATIVE-ENERGY STATES

Negative energy states are included explicitly in relativistic Brueckn er-Hartree-Fock (RBHF) calculations by a medium-modified Gross spectat or equation approach. An important advantage is the unambiguous determ ination of the Dirac and momentum structure of the RBHF self-energy. A pplications to infinite symmetric nuclear matter are discussed. Qualit atively our results are close to conventional RBHF calculations. In de tail, however, significant differences occur. They are related to the fact that a large part of the vector repulsion is generated dynamicall y by the explicit treatment of the negative energy states. The equatio n of state is stiffer and the momentum dependence of the self-energy c omponents is stronger than found in a reference calculation without in termediate negative energy states. The density dependence of effective mean-field coupling constants is found to change considerably when Di rac-sea contributions are included.