Approaching the chiral point in two-flavour lattice simulations

TL;DR

This paper studies the behavior of pion properties in two-flavour lattice QCD near the physical and chiral points, using improved Wilson fermions and exploring chiral perturbation theory applicability.

Contribution

It provides detailed lattice measurements of pion decay constant and mass at low pion masses, and assesses the validity of SU(2) chiral perturbation theory in this regime.

Findings

Pion mass as low as 190 MeV achieved

Chiral perturbation theory applicability range analyzed

Physical scale set via kaon decay constant

Abstract

We investigate the behaviour of the pion decay constant and the pion mass in two-flavour lattice QCD, with the physical and chiral points as ultimate goal. Measurements come from the ensembles generated by the CLS initiative using the O(a)-improved Wilson formulation, with lattice spacing down to about 0.05 fermi and pion masses as low as 190 MeV. The applicability of SU(2) chiral perturbation theory is investigated, and various functional forms, and their range of validity, are compared. The physical scale is set through the kaon decay constant, whose measurement is enabled by inserting a third, heavier valence strange quark.