A comparison between relativistic and semi-relativistic treatment in the diquark–quark model

In the diquark–quark model of the nucleon including scalar and axialvector diquarks we compare solutions of the ladder Bethe–Salpeter equation in the instantaneous Salpeter approximation and in the fully covariant (i.e. four-dimensional) treatment. We obtain that the binding energy is severely underestimated in the Salpeter approximation. For the electromagnetic form factors of the nucleon we find that in both approaches the overall shapes of the respective form factors are reasonably similar up to Q2≈0.4 GeV2. However, the magnetic moments differ substantially as well as results for the pion–nucleon and the axial coupling of the nucleon.