Lattice QCD with the Overlap Fermions at Strong Gauge Coupling (II)

TL;DR

This paper derives a low-energy effective theory for lattice QCD with overlap fermions at strong coupling, demonstrating the emergence of massless pions as Nambu-Goldstone bosons and analyzing their properties and symmetries.

Contribution

It provides a derivation of the hadronic effective action and identifies the pions as nonlocal composite fields with their massless nature at zero quark mass, extending previous work on strong-coupling expansion.

Findings

Existence of quasi-Nambu-Goldstone bosons identified as pions.

Pions are nonlocal composite fields due to overlap fermion formalism.

Pions become massless as bare-quark mass approaches zero.

Abstract

In the previous paper we developed a strong-coupling expansion for the lattice QCD with the overlap fermions and showed that L\"usher's "extended" chiral symmetry is spontaneously broken in some parameter region of the overlap fermions. In this paper, we derive a low-energy effective action of hadrons and show that there exist quasi-Nambu-Goldstone bosons which are identified as the pions. The pion field is a {\em nonlocal} composite field of quark and anti-quark even at the strong-coupling limit because of the nonlocality of the overlap fermion formalism and L\"usher's chiral symmetry. The pions become massless in the limit of the vanishing bare-quark mass as it is desired. We furthermore examine symmetries of the overlap fermions with the hopping expansion and argue that there appear no other massless modes other than the pions.