Tensor Correlations and Pions in Dense Nuclear Matter

The study of tensor correlations and pions in dense matter in astronomical contexts has recently acquired renewed importance for a number of reasons. One is the discovery by Akmal, and Pandharipande (Phys. Rev. C56 2261 (1997)) of a striking increase in tensor correlations in cold matter at densities not far above that of isospin-symmetric nuclear matter at saturation. A second is that, according to a calculation by Mayle and Wilson, softening of the equation of state by the appearance of thermal pions can play an important role. A third is that the strength of tensor correlations is a crucial ingredient in calculating rates of neutrino emission and scattering, which are needed in calculations of stellar collapse and of the cooling of neutron stars. We describe some recent results for the response of nuclear matter when tensor interactions are taken into account, and indicate some unresolved issues.