Topological susceptibility with the improved Asqtad action

TL;DR

This study uses the improved Asqtad lattice fermion action to numerically investigate how light dynamical quarks suppress topological susceptibility in QCD, confirming predictions of chiral perturbation theory.

Contribution

It demonstrates the effectiveness of the Asqtad action in capturing instanton physics and compares three methods for measuring topological susceptibility.

Findings

Results agree with leading order chiral perturbation theory when extrapolated to zero lattice spacing.

The Asqtad action accurately reflects the suppression of topological susceptibility by light quarks.

Comparison of methods shows consistent measurements of topological susceptibility.

Abstract

Chiral perturbation theory predicts that in quantum chromodymamics light dynamical quarks suppress the topological (instanton) susceptibility. We investigate this suppression through direct numerical simulation using the Asqtad improved lattice fermion action. This action holds promise for carrying out nonperturbative simulations over a range of quark masses for which chiral perturbation theory is expected to converge. To test the effectiveness of the action in capturing instanton physics, we measure the topological susceptibility as a function of quark masses with 2+1 dynamical flavors. Our results, when extrapolated to zero lattice spacing, are consistent with predictions of leading order chiral perturbation theory. Included in our study is a comparison of three methods for analyzing the topological susceptibility: (1) the Boulder hypercubic blocking technique with the Boulder topological charge operator, (2) the more traditional Wilson cooling method with the twisted plaquette topological charge operator and (3) the improved cooling method of de Forcrand, Perez, and Stamatescu and their improved topological charge operator.