Nucleon Properties in the Covariant Quark-Diquark Model

Abstract

In the covariant quark-diquark model the effective Bethe-Salpeter (BS) equations for the nucleon and the $Δ$ are solved including scalar {\em and axialvector} diquark correlations. Their quark substructure is effectively taken into account in both, the interaction kernel of the BS equations and the currents employed to calculate nucleon observables. Electromagnetic current conservation is maintained. The electric form factors of proton and neutron match the data. Their magnetic moments improve considerably by including axialvector diquarks and photon induced scalar-axialvector transitions. The isoscalar magnetic moment can be reproduced, the isovector contribution is about 15% too small. The ratio $μG_E/G_M$ and the axial and strong couplings $g_A$, $g_{πNN}$, provide an upper bound on the relative importance of axialvector diquarks confirming that scalar diquarks nevertheless describe the dominant 2-quark correlations inside nucleons.