Hadron Resonances Within a Constituent-Quark Model

In order to get a more realistic description of the hadron spectrum we extend a constituent-quark model by explicit mesonic degrees of freedom. The resulting system of constituent (anti)quarks, which are subject to an instantaneous confining force, and mesons, which couple directly to the quarks, is treated by means of a relativistic coupled-channel framework. It can be formally shown that the mass-eigenvalue problem for such a system is equivalent to a hadronic eigenvalue problem in which the eigenstates of the pure confinement potential (bare hadrons) are coupled via meson loops. Following this kind of approach we have calculated hadron masses and decay widths for a simple toy model.