两U（1）轴子模型
A Tale of Two-U(1) Axion Models
摘要：
解决强$CP$问题的$U(1)$整体对称性可能是QCD和隐藏强动力学的多重$U(1)$对称性的剩余。对Peccei-Quinn $U(1)$和动态$U(1)$进行了统一的描述，并在此基础上对各种混合两$U(1)$模型进行了分类，以解决强$CP$和质量问题。我们提出了一种不同费米子分配的驼鹿图方法来直接读取$CP$相位之间的关系，这说明了如何解决强$CP$问题的$CP$相位之间的抵消。在两种轴子模型中，我们发现最轻的轴子在红外区仍然与QCD轴子相同，而具有$Z_2$对称性的轴子模型则增强了轴子的质量谱。我们的讨论可以扩展到多轴子的情况。
英文摘要：
The $U(1)$ global symmetry to solve the strong $CP$ problem could be the remnant of multi-$U(1)$ symmetries from QCD and hidden strong dynamics. Both Peccei-Quinn $U(1)$ and dynamical $U(1)$ are described uniformly, based on which we classify various mixed two-$U(1)$ models to solve both strong $CP$ and quality problems. We propose a moose diagram method with different fermion assignments to directly read relations between $CP$ phases, which illustrate how strong $CP$ problem is solved in terms of cancellation between $CP$ phases. In two axion models, we find the lightest axion is still same as QCD axion at infrared region, while one axion model with $Z_2$ symmetry enhances the axion mass spectrum. Our discussions can be extended to multi-axion cases.
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