Isospin-breaking corrections to the pion-nucleon scattering lengths

Abstract

We analyze isospin breaking through quark mass differences and virtual photons in the pion-nucleon scattering lengths in all physical channels in the framework of covariant baryon chiral perturbation theory. The so-called triangle relation is found to be violated by about 1.5 %. We encounter a substantial isospin-breaking correction to neutral-pion-nucleon scattering beyond Weinberg's prediction due to a cusp effect. Finally, the application to hadronic atoms is briefly discussed.

Comments: 6 pages, 2 figures, Proceedings for the 6th International Workshop on Chiral Dynamics, Bern, Switzerland, July 6-10, 2009