ASPECTS OF CHIRAL PION-NUCLEON PHYSICS

摘要

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 Delta excitation as well as vector and scalar meson exchange, Ln 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 pi N P-waves. The calculated D- and F-wave threshold parameters compare well with the empirical values. (C) 1997 Elsevier Science B.V. [References: 32]