Low-energy couplings of QCD from current correlators near the chiral limit

TL;DR

This paper introduces a numerical method using low-mode averaging to accurately compute fermionic correlators at very small quark masses, enabling better extraction of low-energy constants in QCD.

Contribution

The paper presents a new numerical technique that reduces statistical fluctuations in correlator computations near the chiral limit, demonstrated with quenched lattice QCD data.

Findings

Agreement between F values from p-regime and epsilon-regime

Successful computation of correlators at small quark masses

Validation of the low-mode averaging technique

Abstract

We investigate a new numerical procedure to compute fermionic correlation functions at very small quark masses. Large statistical fluctuations, due to the presence of local ``bumps'' in the wave functions associated with the low-lying eigenmodes of the Dirac operator, are reduced by an exact low-mode averaging. To demonstrate the feasibility of the technique, we compute the two-point correlator of the left-handed vector current with Neuberger fermions in the quenched approximation, for lattices with a linear extent of L~1.5 fm, a lattice spacing a~0.09 fm, and quark masses down to the epsilon-regime. By matching the results with the corresponding (quenched) chiral perturbation theory expressions, an estimate of (quenched) low-energy constants can be obtained. We find agreement between the quenched values of F extrapolated from the p-regime and extracted in the epsilon-regime.