Improved unitarized Heavy Baryon Chiral Perturbation Theory for π N scattering

Abstract

We show how the unitarized description of pion nucleon scattering within Heavy Baryon Chiral Perturbation Theory can be considerably improved, by a suitable reordering of the expansion over the nucleon mass. Within this framework, the ∆ resonance and its associated pole can be recovered from the chiral parameters obtained from low-energy determinations. In addition, we can obtain a good description of the six S and P wave phase shifts in terms of chiral parameters with a natural size and compatible with the Resonance Saturation Hypothesis.