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 <identifier>oai:arXiv.org:1603.00997</identifier>
 <datestamp>2016-03-04</datestamp>
 <setSpec>physics:hep-lat</setSpec>
 <setSpec>physics:nucl-th</setSpec>
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 <arXiv xmlns="http://arxiv.org/OAI/arXiv/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://arxiv.org/OAI/arXiv/ http://arxiv.org/OAI/arXiv.xsd">
 <id>1603.00997</id><created>2016-03-03</created><authors><author><keyname>Sinya for JLQCD Collaboration</keyname></author></authors><title>Axial U(1) symmetry in the chiral symmetric phase of 2-flavor QCD at
  finite temperature</title><categories>hep-lat nucl-th</categories><comments>10 pages, 5 figures, A talk given at &quot;The 8th International Workshop
  on Chiral Dynamics, CD2015&quot;, 29 June - 03 July, 2015, Pisa, Italy</comments><report-no>YITP-2016-26</report-no><journal-ref>PoS(CD15) (2015) 045</journal-ref><license>http://arxiv.org/licenses/nonexclusive-distrib/1.0/</license><abstract>  We discuss the fate of the axial U(1) symmetry in 2-flavor QCD at finite
temperature, where the non-singlet chiral symmetry is restored. We first
summarize the previous theoretical investigation on the relation between the
eigenvalue density of the Dirac operator and the axial U(1) symmetry. We show
that the eigenvalue density near the origin behaves as $\lambda^\gamma$ with
$\gamma &gt; 2$ in the chirally symmetric phase, where $\lambda$ is an eigenvalue.
This implies that the axial U(1) symmetry is partially restored, so that the
low energy symmetry of the theory becomes SU(2)$\otimes$ SU(2)$\otimes$ Z$_4$.
Secondly, we report recent numerical investigations on this issue by lattice
QCD simulations with lattice chiral fermions such as Overlap or improved
domain-wall fermions. Our preliminary results indicate that the eigenvalue
density seems to have a gap at the origin just above $T_c$, the temperature of
the chiral symmetry restoration, which implies the axial U(1) symmetry is
effectively restored at high temperature. We also point out an importance of
the exact lattice chiral symmetry to obtain correct results on this issue.
</abstract></arXiv>
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