Possible origin of three nucleon interactions

We discuss some aspects of three nucleon interactions (3NI) in nuclei. As is well known, a non-relativistic model with local NN interactions (2NI) alone cannot simultaneously fit two nucleon and nuclear matter properties. A phenomenological 3NI which resolves this problem was suggested by Carlson et al. We then consider two potentials which have the same S-wave phase shift but differ with the respect to their short range interactions, and consequently in their resulting three body ground state energy. Finally, the three nucleon energy can be attributed to a combination of short range correlations and approximate chiral symmetry restoration in nuclear matter. (author)