Space-time dependence of the gluon condensate correlation function and quarkonium spectra

We consider the influence of the gluon condensate in QCD on the energy levels of quarkonia, taking into account the x-dependence of 〈ω|:G_μv^a(x) G^aμv(0):|ω〉. The modification compared to earlier approaches which approxim ated the above vacuum expectation value by a constant is quite sizeable; for the b?b system we find that the effect can be essentially described in terms of a local potential.