Ring diagrams in nuclear matter

Abstract

Ring diagrams in nuclear matter are calculated to all orders using a Bruckner G-matrix derived from a one-boson-exchange NN potential which describes the two-nucleon data accurately. When the conventional choice for the particle and hole potentials in nuclear matter is used, the convergence of the series of ring diagrams is found to be excellent. In these calculations the third order ring diagram turns out to give a positive (i.e. repulsive) contribution to the energy per particle with a strong density dependence of k f 7. This surprising fact, which is in contrast to earlier calculations using simple and too unrealistic forces, is traced back to the large coupling of the ρ-exchange of the NN potential applied in this work. Ring diagrams with intermediate Δ -isobars using π- and ρ-exchange for the relevant forces are aslo calculated. In this case, too, the contribution, which can be interpretated as a contribution from many-body forces, is positive and has the even stronger density dependence of k f 9.