The chiral limit in lattice QCD

TL;DR

This paper discusses overcoming computational challenges in lattice QCD simulations near the chiral limit by using exact chiral symmetry and topology conserving actions, achieving simulations with very light quarks.

Contribution

It introduces a successful approach to simulate two-flavor QCD with near-physical quark masses using modified chiral symmetry and topology conservation.

Findings

Reduced sea quark mass down to a few MeV

Effective use of overlap-Dirac operator and topology conserving action

Demonstrated feasibility of chiral limit simulations

Abstract

It has been a big challenge for lattice QCD to simulate dynamical quarks near the chiral limit. Theoretically, it is well-known that the naive chiral symmetry cannot be realized on the lattice (the Nielsen-Ninomiya theorem). Also practically, the computational cost rapidly grows as the quark mass is reduced. The JLQCD collaboration started a project to perform simulations with exact but modified chiral symmetry using the the overlap-Dirac operator and the topology conserving action. The latter is helpful to reduce the numerical cost of the dynamical quarks. Our simulation of two-flavor QCD has been successful to reduce the sea quark mass down to a few MeV.