Improved unitarized Heavy Baryon Chiral Perturbation Theory for pi N scattering

We show how the unitarized description of pion nucleon scattering within He avy Baryon Chiral Perturbation Theory can be considerably improved, by a su itable reordering of the expansion over the nucleon mass. Within this frame work, 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 term s of chiral parameters with a natural size and compatible with the Resonanc e Saturation Hypothesis. (C) 2000 Elsevier Science B.V. All rights reserved .