Coupling and decoupling of pions and deltas in nuclear matter

We implement the delta-hole model for pions in nuclear matter, including self-consistent real and imaginary self energies for both pions and deltas via dispersion relations cut off by form factors. The real part of the pion inverse propagator vanishes at only one energy for each momentum, unlike the conventional picture of level mixing and level repulsion, because of the width of the delta-hole excitation. Results agree with experiments on baryonic charge-exchange reactions and photo-absorption by heavy nuclei. (orig.)