COVARIANT DESCRIPTION OF THE DELTA IN NUCLEAR-MATTER

To incorporate the DELTA isobar in the relativistic Dirac-Brueckner model we develop a formalism that treats the DELTA analogously to the nucleon. That is, we introduce scalar and vector components of the DELTA self-energy and define effective quantities for the DELTA similar to the ones for the nucleon. Using this formalism and based on one-boson-exchange interactions, we present a parameter-free calculation of the equation of state of nuclear matter. We list results for the effective quantities of both the nucleon and the DELTA. The main result we find is that m our model the properties of the nucleon in nuclear matter seem hardly affected by the inclusion of the DELTA. Also the medium dependence of the properties of the DELTA turns out to be quite small. Finally we investigate the momentum dependence of the mean field of the DELTA.