Bound $q^2{\bar{q}}^2$ states in a constituent quark model

We consider the existence of bound systems consisting of two quarks and two antiquarks ($q^2{\bar{q}}^2$) within the framework of a constituent quark model. The underlying quark dynamics is described by a linear confinement potential and an effective $q^2{\bar{q}}^2$ interaction which has its origin in instanton effects of QCD. We calculate the spectra and examine the internal structure of the states found.