Eckhard Krotscheck (Department of Physics, University at Buffalo SUNY, USA Institut für Theoretische Physik, JKU Linz, Austria)

The most difficult aspect of the nuclear many-body problem is the form of the microscopic nucleon-nucleon interaction which depends at least on the spin, isospin, relative orientation, and angular momentum of the interacting particles. Methods that have proven very successful for simple systems like electrons or the helium liquids are manifestly inadequate. Correlation functions that have the same structure as the interactions lead to so-called “commutator diagrams” that have, so far, been mostly neglected. We show that these corrections can be very important if the two-body interactions are very different in different spin- or isospin channels. In the language of diagrammatic perturbation theory, “commutator diagrams” can be identified with non-parquet diagrams. Calculations are carried out for neutron matter interacting via the so-called v8 version of four popular interactions. We determine the structure and effective interactions and apply the method to the calculation of the energetics, structure, and dynamic properties of neutron matter, such as the single-particle self-energy and the dynamic response functions, as well as BCS pairing in both singlet and triplet states. We find that many-body correlations lead to a strong reduction of the spin-orbit interaction, and, therefore, to an almost complete suppression of the 3P2 and 3P2-3F2 gaps. We also find pairing in 3P0 states; the strength of the pairing gap depends sensitively on the potential model employed