Evidence Against Instanton Dominance of Topological Charge Fluctuations in QCD

TL;DR

This study uses lattice QCD to analyze the chiral structure of low Dirac eigenmodes, providing evidence that topological charge fluctuations in the QCD vacuum are not dominated by instantons, supporting confinement-related origins.

Contribution

The paper offers lattice QCD evidence challenging the instanton dominance hypothesis for topological charge fluctuations in QCD.

Findings

Topological charge fluctuations are not instanton-dominated.

Chiral structure of eigenmodes supports confinement-related fluctuations.

Results align with Witten's confinement-based topological charge production theory.

Abstract

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 $U_A(1)$ problem (i.e. the origin of the $\eta'$ mass), the nature of spontaneous chiral symmetry breaking, and the physics of string-breaking, quark-antiquark pair production, and the OZI rule. Moreover, the space-time chiral structure of these eigenmodes reflects the space-time topological structure of the underlying gauge field. We present evidence from lattice QCD on the local chiral structure of low Dirac eigenmodes leading to the conclusion that topological charge fluctuations of the QCD vacuum are not instanton-dominated. The result supports Witten's arguments that topological charge is produced by confinement-related gauge fluctuations rather than instantons.