Glueballs and instantons

Gluonic correlation functions and Bethe-Salpeter amplitudes are calculated in an instanton-based model of the QCD vacuum. We consider both the pure gauge case and the situation for real QCD with two light quark flavors. We show that instantons lead to a strong attractive force in the JPC=0++ channel, which results in the scalar glueball being much smaller than other glueballs. In the 0-+ channel the corresponding force is repulsive, and in the 2++ case it is absent. The resulting correlators, masses, coupling constants, and wave functions are compared to the results of lattice simulations.