Pion–nucleon scattering in chiral perturbation theory II: Fourth order calculation Original Research Article

We analyze elastic pion–nucleon scattering to fourth order in heavy-baryon chiral perturbation theory, extending the third-order study published in Nucl. Phys. A 640 (1998) 199. We use various partial-wave analyses to pin down the low-energy constants from data in the physical region. The S-wave scattering lengths are consistent with recent determinations from pionic hydrogen and deuterium. We find an improved description of the P-waves. We also discuss the pion–nucleon sigma term and problems related to the prediction of the subthreshold parameters.