Anomalous Chiral Behavior in Quenched Lattice QCD

TL;DR

This paper investigates the anomalous chiral behavior in quenched lattice QCD, demonstrating the presence of quenched chiral logs and quantifying their effects through multiple independent measurements.

Contribution

It provides the first detailed quantitative analysis of quenched chiral logs using MQA and multiple observables, confirming theoretical predictions.

Findings

Accurate pion masses down to 200 MeV using MQA

Quantitative agreement of chiral log effects with eta' hairpin and topological susceptibility measurements

Determination of the quenched chiral log parameter δ as approximately 0.065

Abstract

A study of the chiral behavior of pseudoscalar masses and decay constants is carried out in quenched lattice QCD with Wilson fermions. Using the modified quenched approximation (MQA) to cure the exceptional configuration problem, accurate results are obtained for pion masses as low as $\approx$ 200 MeV. The anomalous chiral log effect associated with quenched $\eta'$ loops is studied in both the relation between $m_{\pi}^2$ vs. $m_q$ and in the light-mass behavior of the pseudoscalar and axial vector matrix elements. The size of these effects agrees quantitatively with a direct measurement of the $\eta'$ hairpin graph, as well as with a measurement of the topological susceptibility, thus providing several independent and quantitatively consistent determinations of the quenched chiral log parameter $\delta$. For $\beta=5.7$ with clover-improved fermions $(C_{sw} =1.57)$ all results are consistent with $\delta=0.065\pm 0.013$ .