Aspects of chiral pion-nucleon physics

V. Bernard, N. Kaiser, Ulf G. Meißner

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The next-to-leading order chiral pion-nucleon Lagrangian contains seven finite low-energy constants. Two can be fixed from the nucleon anomalous magnetic moments and another one from the quark mass contribution to the neutron-proton mass splitting. We find a set of nine observables, which to one-loop order only depend on the remaining four dimension-two couplings. These are then determined from a best fit. We also show that their values can be understood in terms of resonance exchange related to Δ excitation as well as vector and scalar meson exchange. In particular, we discuss the role of the fictitious scalar-isoscalar meson. We also investigate the chiral expansion of the two P-wave scattering volumes P-1 and P+2 as well as the isovector S-wave effective range parameter b- . The one-loop calculation is in good agreement with the data. The difference P-1 - P+2 signals chiral loop effects in the πN P-waves. The calculated D-and F-wave threshold parameters compare well with the empirical values.

Original languageEnglish
Pages (from-to)483-500
Number of pages18
JournalNuclear Physics, Section A
Issue number4
StatePublished - 7 Apr 1997


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