Instanton contributions to the low-lying hadron mass spectrum

TL;DR

This study investigates how instanton-like objects in the QCD vacuum influence the mass spectrum of low-lying light hadrons using lattice QCD with specialized smearing techniques.

Contribution

It demonstrates the impact of instanton content on hadron spectra and compares vacuum configurations at different pion masses, revealing insights into non-perturbative QCD effects.

Findings

Ground-state hadrons are qualitatively preserved on instanton-dominated configurations.

Excited states show significant changes under instanton influence.

Results challenge predictions of the instanton liquid model regarding direct-instanton interactions.

Abstract

The role of instanton-like objects in the QCD vacuum on the mass spectrum of low-lying light hadrons is explored in lattice QCD. Using over-improved stout-link smearing, tuned to preserve instanton-like objects in the QCD vacuum, the evolution of the mass spectrum under smearing is examined. The calculation is performed using a $20^3\times40$ dynamical fat-link-irrelevant-clover (FLIC) fermion action ensemble with lattice spacing 0.126 fm. Through the consideration of a range of pion masses, the effect of the vacuum instanton content is compared at a common pion mass. While the qualitative features of ground-state hadrons are preserved on instanton-dominated configurations, the excitation spectrum experiences significant changes. The underlying physics revealed shows little similarity to the direct-instanton interaction predictions of the instanton liquid model.