Lattice QCD with the overlap fermions at strong gauge coupling (II) Original Research Article

In the previous paper we developed a strong-coupling expansion for the lattice QCD with the overlap fermions and showed that Lüscherʹs “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 nonlocal composite field of quark and anti-quark even at the strong-coupling limit because of the nonlocality of the overlap fermion formalism and Lüscherʹs 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.