How good is the quenched approximation of QCD?

TL;DR

This paper reviews the impact of the quenched approximation in lattice QCD calculations, using chiral perturbation theory to analyze differences and limitations of the approach.

Contribution

It provides a quantitative analysis of quenched versus unquenched QCD effects through an analytic study based on chiral perturbation theory.

Findings

Quantifies differences between quenched and unquenched QCD.

Identifies limitations and issues inherent in quenched QCD.

Offers insights into the diseases affecting quenched QCD.

Abstract

The quenched approximation for QCD is, at present and in the foreseeable future, unavoidable in lattice calculations with realistic choices of the lattice spacing, volume and quark masses. In this talk, I review an analytic study of the effects of quenching based on chiral perturbation theory. Quenched chiral perturbation theory leads to quantitative insight on the difference between quenched and unquenched QCD, and reveals clearly some of the diseases which are expected to plague quenched QCD. Uses jnl.tex and epsf.tex for figure 3. Figures 1 and 2 not included, sorry. Available as hardcopy on request.