Generalized polarizabilities of the proton in a constituent quark model revisited - art. no. 025205

We study low-energy virtual Compton scattering off the proton within the fr amework of a nonrelativistic constituent quark model. The Compton tensor is divided into two separately gauge-invariant contributions. The first consi sts of the ground-state propagation in the direct and crossed channels toge ther with an appropriately chosen term to satisfy gauge invariance. The res idual part contains the relevant structure information characterized by the so-called generalized polarizabilities. We discuss two different schemes t o obtain the generalized polarizabilities from the residual term. Explicit predictions for the generalized polarizabilities are presented for the Isgu r-Karl model. Our results are compared with previous predictions in that mo del as well as other approaches.