Confronting instanton perturbation theory with QCD lattice results

We exploit a recent lattice investigation (UKQCD) on the topological structure of the (quenched) QCD vacuum, in order to gain information on crucial building blocks of instanton perturbation theory. A central motivation is to further constrain our previous predictions of instanton-induced hard scattering processes. First, we address the generic problem of extracting quantitative information from cooled lattice data. We find a new scaling variable, interpreted as a “cooling radius”, which allows to combine lattice data for a whole range of lattice spacings and cooling sweeps. This variable strongly helps to extract information on the uncooled distributions of interest. After performing the continuum extrapolation of the instanton size and instanton-anti-instanton distance distributions, we find striking agreement with the theoretical predictions from instanton-perturbation theory, for instanton sizes ≲0.5 fm and distances ≳0.5 fm, respectively. These results imply first direct support for the validity of the known valley interaction between instantons and anti-instantons.