Accurate nucleon electromagnetic form factors from dispersively improved chiral effective field theory

Abstract

We present a theoretical parametrization of the nucleon electromagnetic form factors (FFs) based on a combination of chiral effective field theory and dispersion analysis. The isovector spectral functions on the two-pion cut are computed using elastic unitarity, chiral pion–nucleon amplitudes, and timelike pion FF data. Higher-mass isovector and isoscalar t-channel states are described by effective poles, whose strength is fixed by sum rules (charges, radii). Excellent agreement with the spacelike proton and neutron FF data is achieved up to Q2∼1 GeV2. Our parametrization provides proper analyticity and theoretical uncertainty estimates and can be used for low-Q2 FF studies and proton radius extraction. Keywords: Nucleon form factors, Proton radius puzzle, Dispersion relations, Chiral effective field theory