Relativistic constituent-quark model of nucleon form factors

We explore the electromagnetic properties of relativistic constituent-quark models of the proton and neutron, in particular their dependence on the constituent-quark mass and the confinement scale. Relativistic effects are never negligible in any model which fits the charge radius of the proton. For a fixed charge radius the confinement scale decreases with decreasing quark masses. Nonvanishing Pauli moments of the constituent quarks are needed to fit the magnetic moments for any value of the quark mass and confinement scale. It is possible to describe existing form-factor data at least up to momentum transfers ${Q}^{2}=6$ Ge${\mathrm{V}}^{2}$ with quark masses significantly smaller than the conventional nonrelativistic choice of about one-third of the nucleon mass.