Resonance Structure of the Pion-Nucleon System

A mechanism giving rise to the spin-orbit forces that have been suggested to produce observed structure in the pi -N cross section is proposed. The exchange of D/sub 13/ is shown to give repulsive forces D/sub 35/ and D/sub 15/ and a probable resonance in D/sub 35/. F/sub 15/ also gives rise to repulsive F/sub 17/ and F/sub 35/ forces and probably an F/sub 37/ resonance. The similarity in shape of the pi /sup -/p and pi /sup +/-p spectra can be understood on the basis of these forces. (D.C.W.)