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

摘要

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 isoscalart-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 toQ2～1GeV2. Our parametrization provides proper analyticity and theoretical uncertainty estimates and can be used for low-Q2FF studies and proton radius extraction.