Abstract:We present an alternative parameterization of the quark-diquark model of baryons which particularly takes care of the most recent proton electric form-factor data from the E136 experiment at SLAC. In addition to electromagnetic form factors of the nucleon, for which good agreement with data is achieved, we discuss the weak axial vector form factor of the nucleon as well as electromagnetic form factors of Λ and Σ hyperons. Technical advance in calculating the pertinent analytic expressions within perturbative quantum chromodynamics is gained by formulating the wave function of the quark-diquark system in a covariant way. Finally, we also comment on the influence of Sudakov corrections within the scope of the diquark model.

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The amplitudes for virtual Compton scattering off protons are calculated within the framework of the diquark model in which protons are viewed as being built up by quarks and diquarks. The latter objects are treated as quasi-elementary constituents of the proton. Virtual Compton scattering, electroproduction of photons and the Bethe-Heitler contamination are discussed for various kinematical situations. We particularly emphasize the rôle of the electron asymmetry for measuring the relative phases between the virtual Compton and the Bethe-Heitler amplitudes. It is also shown that the model is able to describe very well the experimental data for real Compton scattering off protons.

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The diquark model in which protons are viewed as being built up by quarks and diquarks (the latter are treated as quasi-elementary constituents at moderately large momentum transfer) is applied to Compton scattering off protons and combined with similar studies of the electromagnetic form factors of nucleons and of [Formula: see text]. It is demonstrated that the model is able to describe very well the data for these reactions at moderately large values of the momentum transfer with a common set of parameters. We also investigate the helicity dependence of the amplitudes. Very interesting and characteristic predictions for various observables are given. In particular a sizeable transversal polarization of the proton is obtained for Compton scattering.