Electromagnetic structure of the nucleon in local-field theory

Abstract

In analogy to the dispersion-relation method for scattering, the description of nucleon electromagnetic structure by local-field theory is discussed in terms of mass-spectral representations for the form factors. The existence of such representations is made plausible although not proved, and it is shown that the spectral distribution functions are related to scattering amplitudes on the mass shell but sometimes in a nonphysical region. It is argued that the main contributor to the magnetic moment structure in the spectral distribution must be the two-pion state, and an attempt is made to evaluate this contribution in terms of the known behavior of pion-nucleon scattering. A semiquantitative calculation yields results in reasonable agreement with experiment. It is emphasized that the large observed charge radius of the proton does not imply the dominance of the two-pion state in the charge structure. Thus it is not impossible that higher mass configurations supply the isotopic scalar charge needed to explain the small neutron-electron interaction.