A Field-Theoretic Parametrization of Low-Energy Nucleon Form Factors

Abstract

A field-theoretic parametrization is proposed for nucleon electromagnetic form factors at momentum transfer less than 600 MeV. The parametrization is part of a larger effective field theory lagrangian that is Lorentz covariant and chirally symmetric, and that has been used to successfully describe bulk and single-particle properties of medium to heavy mass nuclei. The parametrization is based on vector meson dominance and a derivative expansion of nucleon couplings to the electromagnetic fields. At lowest order in the expansion, it is possible to fit all four parameters to modern data on the rms radii of the nucleon form factors. At next-to-leading order it is possible to fit the form factors to within a few percent up to momentum transfers of 600 MeV. The vector meson dominance contributions are crucial in this fit, since a simple expansion in powers of momentum transfer would require many, many terms to achieve comparable accuracy. The ability to fit single-nucleon form factors up to 600 MeV momentum transfer makes possible the study of two-body electromagnetic exchange currents within this effective field theory framework.