Quenched and Unquenched Chiral Perturbation Theory in the \epsilon-Regime

TL;DR

This paper explores how the epsilon-regime of finite-volume QCD can be utilized to determine low-energy observables by comparing lattice simulations with quenched and unquenched chiral perturbation theories, highlighting issues like quenched finite volume logs.

Contribution

It analyzes the application of quenched and unquenched chiral perturbation theory in the epsilon-regime for extracting QCD low-energy constants, addressing quenched finite volume logs.

Findings

Identification of quenched finite volume logs as a key issue

Comparison framework between lattice data and chiral perturbation theory

Insights into the limitations of quenched approximation in the epsilon-regime

Abstract

The chiral limit of finite-volume QCD is the $\epsilon$-regime of the theory. We discuss how this regime can be used for determining low-energy observables of QCD by means of comparisons between lattice simulations and quenched and unquenched chiral perturbation theory. The quenched theory suffers in the $\epsilon$-regime from ``quenched finite volume logs'', the finite-volume analogs of quenched chiral logs.