Isobar degrees of freedom in nuclei

Abstract

A report is given on some recent investigations of the influence of isobar degrees of freedom on the ground state properties of finite nuclei like e.g. ¹⁶O. The nucleon-nucleon (NN) interaction is constructed in the framework of an extended one-boson-exchange (OBE) model using non-covariant, time-dependent perturbation theory. The explicit consideration of fourth-order iterative diagrams involving NΔ and ΔΔ intermediate states gives an effective NN interaction in the nuclear many-body system which is less attractive than those which are obtained treating these terms phenomenologically. Therefore the binding energy calculated in the Brueckner-Hartree-Fock approximation is smaller if these effects of isobar degrees of freedom are taken into account. This repulsive effect of isobar configurations is partly counterbalanced by the attraction obtained for three-nucleon terms with intermediate NNΔ states.