Role of isobars in nuclear independent particle motion

Multiple meson exchanges proceeding primarily via excitation of isobars can lead to strong many body interactions between nucleons. Three body interactions may be more important in most nuclei than the two body one pion exchange interaction. I will discuss four simple models of nuclear forces, each of which gives nuclear saturation, but which differ importantly in other respects. In actual nuclei, it appears that all four mechanisms play a role, but I would like to explore at least the possibility that the many body forces due to the isobar mechanism are the most important of the four. We will also discuss the implication of the isobar model for some low energy properties of finite nuclei. This model, in conjunction with the condition W = -1/2 Tsub(F) for nuclear matter (which is approximately satisfied) leads to the independent particle model and (approximately) a surface delta residual interaction in finite nuclei. The isobar model differs from most conventional models of nuclear interactions used at present in that it requires a somewhat weaker tensor force. (orig.)