Effect of the Δ(1236) resonance on NN scattering, nuclear matter and neutron matter

A momentum-space nucleon-nucleon potential in the OBE frame is presented where part of the phenomenlogical sigma-contribution describing the intermediate range attraction is replaced by the twice-iterated pion-exchange potentials which couple the NN channel with the NΔ(1236) and ΔΔ channels. For various strengths of these transition potentials (depending on a cutoff parameter), a sufficiently accurate description of NN data is obtained. These models are then used to calculate nuclear matter properties in first-order Brueckner theory. Due to the explicit treatment of the Δ, there is a strong repulsive effect in all partial wave states. It turns out, however, that one does not come off the Coester band. In addition, neutron matter calculations at densities relevant for neutron stars are presented. It turns out that 80% of the total repulsive effect introduced by the Δ arises in L>=1 partial wave states. (Auth.)