Abstract
We investigate the axial U(1)A symmetry breaking above the critical temperature in two-flavor lattice QCD. The ensembles are generated with dynamical Möbius domain-wall or reweighted overlap fermions. The U(1)A susceptibility is extracted from the low-modes spectrum of the overlap Dirac eigenvalues. We show the quark mass and temperature dependences of U(1)A susceptibility. Our results at T = 220MeV imply that the U(1)A symmetry is restored in the chiral limit. Its coincidence with vanishing topological susceptibility is observed.
Highlights
In quantum chromodynamics (QCD) at low temperature, the axial U(1)A symmetry is violated by the quantum anomaly, which is the origin of much heavier η meson than other pseudoscalar mesons
Where a is the isospin index. (We consider the theory with two degenerate quark flavors.) Above the critical temperature, T > Tc, while the chiral symmetry is known to be restored, the restoration/violation of the U(1)A symmetry is a long standing problem, which has been studied using in analytic methods [1,2,3] and effective theories [4, 5] as well as lattice QCD simulations at N f = 2 [6,7,8,9] and N f = 2 + 1 [10,11,12,13]
The coarser lattice leads to larger violation of the GW relation for Möbius DW fermion [17], we found that Δoπv−δ is suppressed for the small quark mass region
Summary
In quantum chromodynamics (QCD) at low temperature, the axial U(1)A symmetry is violated by the quantum (chiral) anomaly, which is the origin of much heavier η meson than other pseudoscalar mesons. Because of the restoration of U(1)A symmetry in the chiral limit for N f = 2, the chiral phase transition at mu,d = 0 may be first-order rather than the (usually expected) secondorder 1 If this is the case, a nonzero “critical mass,” mcur,di , appears, which separates the first-order region m < mcur,di and the crossover region m > mcur,di for N f = 2. Since the Ginsparg-Wilson (GW) relation [16] for the Möbius domain-wall fermion is slightly violated especially for larger lattice spacings [17], we applied the domain-wall/overlap reweighting [9], where an observable on the gauge ensembles generated with dynamical domain-wall fermions is reweighted to that of overlap fermions.
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