Effects of direct nucleon-nucleon interactions in pion-condensed neutron star matter

We investigate the effects of direct nucleon-nucleon interactions in the ground state of pion-condensed neutron star matter within the sigma-model formalism. We use a realistic description of asymmetric nuclear matter. The divergence of the critical density as g/sub A/ approaches 1.0 is removed by including direct nucleon-nucleon forces. For the most realistic equations of state, we find a density interval with negative pressure from the critical density up to approximately 0.5 N/fm/sup 3/, preventing a pion condensate below this density. The most realistic equations of state are considerably softer than ..beta..-stable neutron star matter. The equations of state show similar behavior for both kinds of chiral symmetry breaking investigated in this calculation. The composition of the matter depends to some extent on the chiral symmetry breaking term in the Hamiltonian. The indicated proton percentage in the allowed density region is higher than 30.