Pion--Nucleon Scattering in a New Approach to Chiral Perturbation Theory
Abstract
We study pion--nucleon scattering with a chiral lagrangian of pions, nucleons, and
Δ
-isobars. The scattering amplitude is evaluated to one-loop
Q
3
order, where
Q
is a generic small momentum, using a new approach which is equivalent to heavy baryon chiral perturbation theory. We obtain a good fit to the experimental phase shifts for pion center-of-mass kinetic energies up to 100 MeV. A sigma term greater than 45 MeV is favored, but the value is not well determined.