Topological susceptibility with the asqtad action

TL;DR

This study measures the topological susceptibility in lattice QCD with asqtad fermions, confirming theoretical predictions and supporting the validity of the fourth-root procedure in staggered fermion formulations.

Contribution

It provides the first large-scale lattice QCD measurement of topological susceptibility with 2+1 flavors of dynamical asqtad quarks, validating chiral perturbation theory predictions.

Findings

Results agree with chiral perturbation theory at small quark masses.

Continuum extrapolation supports the validity of the fourth-root procedure.

Measurements span various lattice spacings and quark masses.

Abstract

Chiral perturbation theory predicts that in quantum chromodynamics (QCD), light dynamical quarks suppress the gauge-field topological susceptibility of the vacuum. The degree of suppression depends on quark multiplicity and masses. It provides a strong consistency test for fermion formulations in lattice QCD. Such tests are especially important for staggered fermion formulations that lack a full chiral symmetry and use the "fourth-root" procedure to achieve the desired number of sea quarks. Over the past few years we have measured the topological susceptibility on a large database of 18 gauge field ensembles, generated in the presence of 2+1 flavors of dynamical asqtad quarks with up and down quark masses ranging from 0.05 to 1 in units of the strange quark mass and lattice spacings ranging from 0.045 fm to 0.12 fm. Our study also includes three quenched ensembles with lattice spacings ranging from 0.06 to 0.12 fm. We construct the topological susceptibility from the integrated point-to-point correlator of the discretized topological charge density F-Fdual. To reduce its variance, we model the asymptotic tail of the correlator. The continuum extrapolation of our results for the topological susceptibility agrees nicely at small quark mass with the predictions of lowest-order SU(3) chiral perturbation theory, thus lending support to the validity of the fourth-root procedure.