1209.2061 (Sinya Aoki et al.)

Chiral symmetry restoration, eigenvalue density of Dirac operator and
axial U(1) anomaly at finite temperature    [PDF]

Sinya Aoki, Hidenori Fukaya, Yusuke Taniguchi

We reconsider constraints on the eigenvalue density of the Dirac operator in the chiral symmetric phase of 2 flavor QCD at finite temperature. To avoid possible ultra-violet(UV) divergences, we work on a lattice, employing the overlap Dirac operator, which ensures the exact "chiral" symmetry at finite lattice spacings. Studying multi-point correlation functions in various channels and taking their thermodynamical limit (and then taking the chiral limit), we obtain stronger constraints than those found in the previous studies: not only the eigenvalue density at the origin but also its first and second derivatives vanish in the chiral limit of 2 flavor QCD. In addition we show that the axial U(1) anomaly becomes invisible in susceptibilities of scalar and pseudo scalar mesons, suggesting that the chiral phase transition is likely to be of first order in 2 flavor QCD. Possible lattice artifacts when non-chiral lattice Dirac operator is employed are briefly discussed.

View original: http://arxiv.org/abs/1209.2061