Extended coupled channels model for πN scattering and the structure of N*(1440) and N*(1535)

We present a coupled channels model for pi N scattering based on N, Delta, and N-S11*(1535) pole and nonpole contributions, plus correlated 2 pi and a(0) meson exchange. The open channels considered are pi N, eta N, sigma N, and pi Delta. The model gives a qualitatively good fit to the phase shifts and elasticity parameters in both isospin channels for partial waves up to J=3/2 and pi N c.m. energies of 1.4 GeV. Above that energy the appearance of resonances in various partial waves precludes a precise fit to the data without explicitly including resonances in those partial waves and-probably-additional inelastic channels. Within the model the N-S11(1.535) reson ance appears to require a genuine three-quark component, whereas the N-P11*(1440) resonance appears to permit description as a purely dynamical effect.