Unquenching the Quark Model

The formalism for a new generation of unquenched quark models for baryons in which the effects of quark-antiquark pairs are taken into account in an explicit form via a microscopic, QCD-inspired, quark-antiquark creation mechanism, is presented. As an application the quark-antiquark contribution to the spin of the proton and the Σ+ is discussed. Finally the strangeness radius of the Σ+ in the closure limit is calculated. Here, we have presented a new generation of unquenched quark models for baryons, in which uu-bar, dd-bar and ss-bar loops are included, with also the possibility to sum, up to saturation, over a complete set of states. In an application to the spin of the Σ+, we have showed that the inclusion of the qq-bar pairs determines an important contribution of orbital angular momentum to the spin of the Σ+.We hope to address with this method different open problems, such as, among others, the strange magnetic moments and the strangeness radii of baryons. (author)