Abstract:
We introduce a relativistic model for pion-nucleon scattering which includes an elementary
delta dressed by its decay. Crossing-symmetric single-particle exchange
is augmented by parametrized multiple-scattering interactions, with covariant sideways
form factors in both 3- and 4-field vertices. Causality is enforced by dispersion
relations. Unitary fits to observed on-shell amplitudes are obtained; a modest number
of parameters precisely reproduce all 6 S- and P-wave π-N amplitudes up to
1.36 GeV invariant mass.
