Scalar mesons, glueballs, instantons and the glueball/sigma

We include instanton effects in QCD sum rules for coupled scalar glueballs and mesons. We find a 400–600 MeV glueball as in earlier studies without instantons, and a possible explanation in terms of high-dimensional condensates for current lattice calculations not finding this glueball/sigma. In the 1–2 GeV region we now find that lightest I=0 meson, in the region of the f0(1370), has no direct glueball mixing, with the instanton loop replacing the glueball component. The lightest scalar mainly glueball in the region of the f0(1500) is sensitive to the choice of nonperturbative gluonic parameters.