Unitarity corrections to a low-energy pion–nucleon scattering amplitude

A method is present to unitarize a low energy pion–nucleon scattering amplitude. Starting from a soft-pion result, we have used unitarity directly as a dynamical constraint and constructed amplitudes from their first-order discontinuities. There is no commitment to the existence of resonances, but they can be derived from the general structure of the model. Working with two parameters we determine low energy πN amplitudes. We have fixed the two parameters of the model by fitting the experimental P 33 phase shifts near 90°. Five S - and P -wave phase shifts are then shown to agree qualitatively with experimental data.