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On-Shell Approach to Pion-Nucleon Physics

James V. Steele, Hidenaga Yamagishi, Ismail Zahed

hep-pharXiv:hep-ph/9707399

Abstract

We discuss an on-shell approach to pion-nucleon physics that is consistent order by order in a 1/fπ expansion with the chiral reduction formula, crossing, and relativistic unitarity. A number of constraints between the on-shell low-energy parameters are derived at tree level in the presence of the pion-nucleon sigma term, and found to be in fair agreement with experiment. We analyze the nucleon form factors, and the πN πN scattering amplitude to one-loop, as well as πNππN to tree level. We use the latter to derive a new constraint for the pion-nucleon sigma term at threshold. We compare our results to both relativistic and non-relativistic chiral perturbation theory, and discuss the convergence character of the expansion in light of experiment.

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