ROLE OF THE DELTA-POTENTIAL IN THE NUCLEAR-MATTER SATURATION MECHANISM

The dependence of the nuclear-matter saturation properties on the potential felt by the virtually excited DELTA-isobar in the medium is studied in the framework of the Bethe-Brueckner-Goldstone method at the two-hole level of approximation. A microscopic realistic two-body interaction, the Argonne upsilon28, which introduces at a minimal level all possible transitions from NN states to NDELTA and DELTADELTA ones, was used. The possibility that the isobar decays in the piN channel is treated in an approximate way by considering the DELTA mass shift in nuclear matter. While the DELTA self-energy turns out to be strongly repulsive near the saturation density, the equation of state of nuclear matter seems to need an attractive DELTA-potential in order to reduce the discrepancy with the empirical saturation point. In particular a potential of magnitude comparable with the nucleon one is able to lower the saturation curve of a few MeV. A potential of such a magnitude is consistent with the experimental data on DELTA-production in nuclei, but cannot be obtained from a simple NN interaction where the short- and intermediate-range parts of the NDELTA and DELTADELTA interactions are determined only by central operators with parameters like the NN ones.