Hook Anson
School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540, USA.
Phys Rev Lett. 2015 Apr 10;114(14):141801. doi: 10.1103/PhysRevLett.114.141801. Epub 2015 Apr 9.
We present a new mechanism for solving the strong CP problem using a Z_{2} discrete symmetry and an anomalous U(1) symmetry. A Z_{2} symmetry is used so that two gauge groups have the same theta angle. An anomalous U(1) symmetry makes the difference between the two theta angles physical and the sum unphysical. Two models are presented where the anomalous symmetry manifests itself in the IR in different ways. In the first model, there are massless bifundamental quarks, a solution reminiscent of the massless up quark solution. In the IR of this model, the η^{'} boson relaxes the QCD theta angle to the difference between the two theta angles-in this case zero. In the second model, the anomalous U(1) symmetry is realized in the IR as a dynamically generated mass term that has exactly the phase needed to cancel the theta angle. Both of these models make the extremely concrete prediction that there exist new colored particles at the TeV scale.
我们提出了一种利用(Z_2)离散对称性和反常(U(1))对称性来解决强(CP)问题的新机制。使用(Z_2)对称性以便两个规范群具有相同的(\theta)角。反常(U(1))对称性使两个(\theta)角之间的差值具有物理意义，而它们的和没有物理意义。我们给出了两个模型，其中反常对称性在红外区域以不同方式表现出来。在第一个模型中，存在无质量的双基本夸克，这是一种让人联想到无质量上夸克解的解决方案。在该模型的红外区域，(\eta^{'})玻色子将量子色动力学的(\theta)角弛豫到两个(\theta)角的差值——在这种情况下为零。在第二个模型中，反常(U(1))对称性在红外区域表现为一个动态生成的质量项，其相位恰好能抵消(\theta)角。这两个模型都做出了非常具体的预测，即在太电子伏特尺度存在新的带色粒子。
