The Dynamical Structure of the Delta-Resonance and its Effect on Two-   and Three-Nucleon Systems
  The pion-nucleon interaction in the P33 partial wave is assumed to proceed simultaneously through the excitation of the Delta-isobar and through a phenomenologically introduced non-resonant background potential. The introduction of the background potential allows a more realistic parameterization of the pion-nucleon-Delta vertex compared with the previously used one without background. It also modifies the propagation of the Delta-isobar in the nuclear medium and gives rise to novel effective nucleon-Delta interactions. Their consequences on predictions for observables in the two-nucleon system at intermediate energies and in the three-nucleon bound state are studied. 
G. Kortemeyer, M. T. Pena, P. U. Sauer, and A. Stadler