Nature of chiral phase transition in two-flavor QCD

We investigate the nature of the chiral phase transition in the massless two-flavor QCD using the renormalization group improved gauge action and the Wilson quark action on 32^3× 16, 24^3× 12, and 16^3× 8 lattices. We calculate the spacial and temporal propagators of the iso-triplet mesons in the pseudo-scalar (PS), scalar (S), vector (V) and axial-vector (AV) channels on the lattice of three sizes. We first verify that the RG scaling is excellently satisfied for all cases. This is consistent with the claim that the chiral phase transition is second order. Then we compare the spacial and temporal effective masses between the axial partners, i.e. PS vs S and V vs AV, on each of the three size lattices. We find the effective masses of all of six cases for the axial partners agree remarkably. This is consistent with the claim that at least Z_4 subgroup of the U_A(1) symmetry in addition to the SU_A(2) symmetry is recovered at the chiral phase transition point.