Nelson-Barr模型中无反常类轴子粒子
Anomaly-free axion-like particle in Nelson-Barr models
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中文总结 AI 辅助
本文研究具有离散Zₙ对称性的Nelson-Barr模型，预言了无反常类轴子粒子，分析其两种宇宙学产生机制的参数空间约束，指出多类观测可互补探测该粒子及Nelson-Barr的强CP问题解决方案。
中文摘要 AI 辅助
我们研究具有离散Zₙ对称性的Nelson-Barr模型，该模型通过自发CP破缺解决强CP问题，且表明这类模型自然预言了一种轻的类轴子粒子（ALP），无需引入任何额外组分。与QCD轴子不同，该ALP是无反常的：它与光子和胶子的耦合被高度压低，使其自然具有长寿命。相反，它通过由CKM矩阵决定结构的味改变相互作用与夸克耦合，这些相互作用会诱导稀有介子衰变，为探测Nelson-Barr机制提供了独特手段。我们研究该ALP通过冻入（freeze-in）和错位（misalignment）机制的宇宙学产生，发现冻入机制能解释观测到的遗迹丰度的参数空间受到精确味实验和SN1987A的恒星冷却限制的严格约束，仅剩下小部分可行区域，将被Vera Rubin天文台等未来结构形成观测以及Athena、GECCO和THESEUS等下一代X射线任务全面检验；相比之下，错位产生机制在广泛的参数空间内仍然是解释观测到的暗物质丰度的可靠且可行的机制。我们的结果表明，精确味测量、宇宙学观测和X射线搜索为这种无反常ALP以及Nelson-Barr对强CP问题的解决方案提供了互补的探测手段。
英文摘要
We study Nelson--Barr models with a discrete $Z_N$ symmetry that solve the strong CP problem through spontaneous CP violation, and show that they naturally predict a light axion-like particle (ALP) without introducing any additional ingredients. Unlike the QCD axion, this ALP is anomaly-free: its couplings to photons and gluons are highly suppressed, rendering it naturally long-lived. Instead, it couples to quarks through flavor-violating interactions whose structure is dictated by the CKM matrix. These interactions induce rare meson decays, providing a unique probe of the Nelson--Barr mechanism. We study the cosmological production of the ALP through both freeze-in and misalignment mechanisms. We show that the parameter space in which the observed relic abundance is explained by the freeze-in mechanism is subject to stringent constraints from precision flavor experiments and stellar cooling bounds from SN1987A, leaving only a small viable region that will be comprehensively tested by future structure-formation observations such as the Vera Rubin Observatory and next-generation X-ray missions like Athena, GECCO and THESEUS. In contrast, misalignment production remains a robust and viable mechanism for explaining the observed dark matter abundance over a broad region of parameter space. Our results demonstrate that precision flavor measurements, cosmological observations, and X-ray searches provide complementary probes of this anomaly-free ALP and, consequently, of the Nelson--Barr solution to the strong CP problem.
