Chiral properties of domain-wall quarks in quenched QCD

We investigate the chiral properties of quenched domain-wall QCD (DWQCD) at the lattice spacings a(-1) similar or equal to 1 and 2 GeV for both plaquette and renormalization-group (RG) improved gauge actions. In the case of the plaquette action we find that the quark mass defined through the axial Ward-Takahashi identity remains non-vanishing in the DWQCD chiral limit that the bare quark mass m(f)-->0 and the length of the fifth dimension N-s--> infinity, indicating that chiral symmetry is not realized with quenched DWQCD up to a(-1) similar or equal to 2 GeV. The behavior is much improved for the RG-improved gauge action: while a nonvanishing quark mass remains in the chiral limit at a(-1) similar or equal to 1 GeV, the result at a(-1) similar or equal to 2 GeV is consistent with an exponentially vanishing quark mass in the DWQCD chiral limit, indicating the realization of exact chiral symmetry. An interpretation and implications are briefly discussed