Chiral Perturbation Theory and the Quenched Approximation of QCD

TL;DR

This paper reviews how chiral perturbation theory helps analyze the effects and limitations of the quenched approximation in lattice QCD calculations, highlighting differences and issues.

Contribution

It provides a detailed analytical framework using quenched chiral perturbation theory to understand quenched QCD and its discrepancies from unquenched QCD.

Findings

Quantitative insights into quenched vs. unquenched QCD differences

Identification of diseases affecting quenched QCD

Clarification of chiral perturbation theory principles

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 these lectures, I review the analytic study of the effects of quenching based on chiral perturbation theory. Quenched chiral perturbation theory leads to quantitative insight into the difference between quenched and unquenched QCD, and reveals clearly diseases which plague quenched QCD. A short review of the ideas underlying chiral perturbation theory is included.