S-WAVE PI-PI-CORRELATIONS IN DENSE NUCLEAR-MATTER

The s-wave correlated pipi strength distribution in cold nuclear matter is investigated. The in-medium single pions are renormalized by means of the usual p-wave couplings to nucleons and DELTA's. Two groups of models for the pipi interaction are studied. The first one uses phenomenological models which reproduce the phase shifts but do not respect the soft-pion theorems. With increasing density a strong accumulation of strength in the subthreshold region is observed. Slightly above saturation density there even occurs an instability with respect to s-wave pipi pair condensation. These effects are strongly moderated or disappear altogether if constraints from chiral symmetry are built into the pipi interaction.