UNITARY, RELATIVISTIC RESONANCE MODEL FOR PI-N SCATTERING

Pion nucleon scattering up to 600 MeV laboratory kinetic energy is described by a manifestly covariant wave equation in which the pion is restricted to its mass shell. The kernel of the equation includes nucleon (N), Roper (N*), delta (A), and D13 poles, with their corresponding crossed pole terms approximated by contact interactions, and contact sigma- and rho-like exchange terms. The piNN vertex is treated as a mixture of gamma5 and gamma(mu)gamma5 coupling, with a mixing parameter lambda chosen so that the dressed nucleon pole will be unshifted by the interaction. Chiral symmetry is maintained at threshold. The resonance contributions are fully unitarized by the equation, with their widths determined by the dynamics included in the model. The DELTA and D13 are treated as a pure spin 3/2 particles, with no spin 1/2 amplitude in the S channel. The complete development of this model, which gives a very good fit to all the data up to 600 MeV, is presented.