paper

Chiral Effective-Field Theory in the Delta(1232) Region: Pion Electroproduction on the Nucleon

arXiv:hep-ph/0512244 · doi:10.1103/PhysRevD.73.034003

Abstract

We develop an extension of chiral perturbation theory to the (1232)-resonance energy region and apply it to investigate the pion electroproduction off the nucleon (). We present a complete calculation of this process, in the -resonance region, up to next-to-leading order in the {\it -expansion}. At this order, the only free parameters are the three low-energy constants corresponding to the magnetic (M1), electric (E2), and Coulomb (C2) transition strength. After fitting these parameters to a few well-known data, our calculation provides a prediction for observables and multipole amplitudes of pion electroproduction. These results compare favorably with the phenomenological multipole solutions and recent experimental results from MIT-Bates and MAMI. Our prediction for the pion-mass dependence of the form factors offers an explanation for the discrepancy between the recent lattice-QCD results and the experimental value for the "C2/M1 ratio" at low .

38 pages, 14 figures; version to be published in Phys. Rev. D

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