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

The dependence of the nuclear-matter saturation properties on the pote ntial felt by the virtually excited DELTA-isobar in the medium is stud ied in the framework of the Bethe-Brueckner-Goldstone method at the tw o-hole level of approximation. A microscopic realistic two-body intera ction, 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 tr eated in an approximate way by considering the DELTA mass shift in nuc lear matter. While the DELTA self-energy turns out to be strongly repu lsive near the saturation density, the equation of state of nuclear ma tter seems to need an attractive DELTA-potential in order to reduce th e discrepancy with the empirical saturation point. In particular a pot ential of magnitude comparable with the nucleon one is able to lower t he saturation curve of a few MeV. A potential of such a magnitude is c onsistent with the experimental data on DELTA-production in nuclei, bu t cannot be obtained from a simple NN interaction where the short- and intermediate-range parts of the NDELTA and DELTADELTA interactions ar e determined only by central operators with parameters like the NN one s.