Improved Unitarized Heavy Baryon Chiral Perturbation Theory for $\pi N $   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. 
A. G\'omez Nicola (1), J. Nieves (2), J.R. Pel\'aez (1) and E. Ruiz   Arriola(2) ((1) Departamento de Fisica Moderna, Univer...