The low-energy constants of the pion-nucleon system

Abstract

Recent analyses of low-energy pion-nucleon experimental data have provided clear evidence for the violation of the isospin symmetry of the strong interaction. In the present work, it is shown that the single-charge-exchange reaction is the culprit for the effect. Given the present experimental uncertainties, no evidence for isospin breaking was found in the two elastic-scattering processes for pion laboratory kinetic energies between 20 and 100 MeV. In agreement with most of the recent determinations, the value for the charged-pion coupling constant, extracted herein, is `small'. The energy dependence of the s- and p-wave hadronic phase shifts, obtained from low-energy elastic-scattering data exclusively, as well as their values in tabular form (including meaningful uncertainties), are provided. Discrepancies with two `standard' phase-shift solutions in the s-wave part of the interaction are seen; small differences may be observed in three of the p-wave channels.