Improved unitarized Heavy Baryon Chiral Perturbation Theory for πN scattering

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 Delta 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. (C) 2000 Elsevier Science B.V. All rights reserved.