Evidence for hard chiral logarithms in quenched lattice QCD

TL;DR

This study provides the first direct lattice QCD evidence that quenched QCD exhibits chiral logarithms differing from full QCD, confirming predictions of quenched chiral perturbation theory through hadron spectrum analysis.

Contribution

It offers the first direct lattice QCD evidence of quenched QCD's deviation from full QCD in the chiral limit, validating quenched chiral perturbation theory predictions.

Findings

Observed logarithmic violations of the PCAC relation in pion masses.

Volume dependence rules out finite size effects.

No chiral logarithms detected in the chiral condensate.

Abstract

We present the first direct evidence that quenched QCD differs from full QCD in the chiral ($m_q \rightarrow 0$) limit, as predicted by chiral perturbation theory, from our quenched lattice QCD simulations at $\beta = 6/g^2 = 6.0$. We measured the spectrum of light hadrons on $16^3 \times 64$, $24^3 \times 64$ and $32^3 \times 64$, using staggered quarks of masses $m_q=0.01$, $m_q=0.005$ and $m_q=0.0025$. The pion masses showed clear evidence for logarithmic violations of the PCAC relation $m_{\pi}^2 \propto m_q$, as predicted by quenched chiral perturbation theory. The dependence on spatial lattice volume precludes this being a finite size effect. No evidence was seen for such chiral logarithms in the behaviour of the chiral condensate $\langle\bar{\psi}\psi\rangle$.