ELECTROMAGNETIC EXCITATIONS IN THE CONSTITUENT QUARK-MODEL

The description of the electromagnetic properties of baryons with explicit reference to the quark degrees of freedom is reviewed. After a short discussion of the available phenomenological information, such as magnetic moments, form factors and photoexcitation amplitudes, the constituent quark model in the potential approach is introduced and the consequent description of the baryon spectrum is briefly discussed. The model is then systematically used as a theoretical framework for the interpretation of the experimental baryon data, including photon-proton scattering and pion photoproduction, and for the discussion of recent studies of the electromagnetic properties of few-nucleon systems. In particular, the reformulation of meson exchange currents in terms of quark degrees of freedom is reported and the results of various quark approaches to the form factors are presented. Finally, some recent improvements and future developments are briefly discussed.