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 ${J}^{\mathrm{PC}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0}^{++}$ channel, which results in the scalar glueball being much smaller than other glueballs. In the ${0}^{\ensuremath{-}+}$ 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.

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