有限温度下QCD $U_A(1)$的命运和拓扑特征

Sayantan Sharma
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引用次数: 8

摘要

具有两种轻夸克口味的QCD的手性相变性质尚未完全解决。这主要是因为人们必须了解风味部分的异常U(1)对称性是否与手性对称性一起有效地恢复了。由于靠近手性相变的物理本质上是非微扰的,我们采用第一性原理晶格技术来解决这个问题。利用在晶格上具有精确手性对称的重叠费米子,研究了具有畴壁费米子的2+1味动态QCD构型的U(1)对称性异常违逆。后者还最佳地保留了晶格上的手性和风味对称性。我们观察到异常的U(1)在手性交叉区没有得到有效的恢复。由于U(1)违背的信号对其敏感,我们对有限尺寸和截止效应进行了系统的研究。出于同样的原因,我们还比较了从不同的晶格离散化(称为高度改进的交错夸克)获得的QCD狄拉克谱的连续介质外推结果。我们的研究还提供了QCD介质的微观拓扑结构的一瞥,这些结构负责夸克胶子等离子体相的强相互作用性质,并与限制和手性对称性破缺的物理有关。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
The fate of $U_A(1)$ and topological features of QCD at finite temperature
The nature of chiral phase transition for QCD with two light quark flavors is not yet completely resolved. This is primarily because one has to understand whether or not the anomalous U(1) symmetry in the flavor sector is effectively restored along with the chiral symmetry. Since the physics near the chiral phase transition is essentially non-perturbative, we employ first principles lattice techniques to address this issue. We use overlap fermions, which have exact chiral symmetry on the lattice, to probe the anomalous U(1) symmetry violation of 2+1 flavor dynamical QCD configurations with domain wall fermions. The latter also optimally preserves chiral and flavor symmetries on the lattice. We observe that the anomalous U(1) is not effectively restored in the chiral crossover region. We perform a systematic study of the finite size and cut-off effects since the signals of U(1) violation are sensitive to it. For the same reasons we also compare our results from the continuum extrapolated results of the QCD Dirac spectrum obtained from a different lattice discretization called Highly Improved Staggered Quarks. Our studies also provide a glimpse of the microscopic topological structures of the QCD medium that are responsible for the strongly interacting nature of the quark gluon plasma phase and related to the physics of confinement and chiral symmetry breaking.
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