QCD mixing effects in a gauge-invariant quark model for photo- and electroproduction of baryon resonances

The photo- and electroproduction of baryon resonances are calculated in the constituent quark model with chromodynamics of Isgur and Karl consistently to $O\left(\frac{v^2}{c^2}\right)$ for the quarks. We find that the successes of the nonrelativistic quark model are preserved, some problems are removed, and QCD mixing effects may become important with increasing $q^2$ in electroproduction. For the first time both spectroscopy and transitions receive a unified treatment within the framework of a potential quark model.