Evidence against instanton dominance of topological charge fluctuations in QCD

The low-lying eigenmodes of the Dirac operator associated with typical gauge field configurations in QCD encode, among other low-energy properties, the physics behind the solution to the ${\mathrm{U}}_A\mathrm{}\left(1\right)\mathrm{}$ problem (i.e., the origin of the ${\eta }^{\prime }$ mass), the nature of spontaneous chiral symmetry breaking, the physics of string-breaking, quark-antiquark pair production, and the Okubo-Zweig-Iizuka (OZI) rule. Moreover, the space-time chiral structure of these eigenmodes reflects the space-time topological structure of the underlying gauge field. We discuss initial evidence from lattice QCD on the local chiral structure of low Dirac eigenmodes which suggests that topological charge fluctuations of the QCD vacuum are not instanton dominated. Such a conclusion would support Witten’s arguments that topological charge is produced by confinement-related gauge fluctuations rather than instantons.