Nuclear and Neutron Matter Calculations with Different Model Spaces

In this work we investigate the so-called model-space Brueckner-Hartree-Fock (MBHF) approach for nuclear matter as well as for neutron matter and the extension of this which includes the particle-particle and hole-hole (PPHH) diagrams. A central ingredient in the model-space approach for nuclear matter is the boundary momentum kM beyond which the single-particle potential energy is set equal to zero. This is also the boundary of the model space within which the PPHH diagrams are calculated. It has been rather uncertain which value should be used for kM . We have carried out model-space nuclear matter and neutron matter calculations with and without PPHH diagrams for various choices of kM and using several modern nucleon-nucleon potentials. Our results exhibit a saturation region where the nuclear and neutron matter matter energies are quite stable as kM varies. The location of this region may serve to determine an ”optimum” choice for kM . However, we find that the strength of the tensor force has a significant influence on binding energy variation with kM . The implications for nuclear and neutron matter calculations are discussed.