用超导辐射腔探测ALP和轴宇宙
Probing ALPs and the Axiverse with Superconducting Radiofrequency Cavities
摘要：
具有电磁耦合的类轴子粒子（ALP）长期以来一直被假定为标准模型的扩展。弦论预言了一个由许多轻轴子组成的“轴宇宙”，其中一些可能构成宇宙中的暗物质和/或解决强CP问题。我们提出了一个新的实验，使用超导射频（SRF）腔，这是敏感的光ALP独立的宇宙暗物质密度的贡献。壳外ALP将产生麦克斯韦方程中的立方非线性，使得如果SRF腔以频率$ω_1$和$ω_2$泵浦，则在ALP存在的情况下，将存在具有频率$2ω_1 \pm ω_2$的模式中的功率。我们的设置在精神上类似于光穿透墙壁（LSW）实验，但由于泵浦场本身有效地将ALP转换回单个腔体内的光子，我们的灵敏度随外部场的强度而不同，与OSQAR等实验相比，在利用现有技术的同时，可以实现更高的范围。此外，一个定义明确的增加灵敏度的计划有一个有保证的物理结果：在低于电子质量的能量下首次观察到低能QED的欧拉-海森堡项。我们讨论了如何ALP的贡献可以从QED的贡献，通过一个合适的选择泵模式和腔的几何形状，并得出结论，通过描述我们提出的方案的实验ALP的最终灵敏度。
英文摘要：
Axion-like particles (ALPs) with couplings to electromagnetism have long been postulated as extensions to the Standard Model. String theory predicts an "axiverse" of many light axions, some of which may make up the dark matter in the universe and/or solve the strong CP problem. We propose a new experiment using superconducting radiofrequency (SRF) cavities which is sensitive to light ALPs independent of their contribution to the cosmic dark matter density. Off-shell ALPs will source cubic nonlinearities in Maxwell's equations, such that if a SRF cavity is pumped at frequencies $ω_1$ and $ω_2$, in the presence of ALPs there will be power in modes with frequencies $2ω_1 \pm ω_2$. Our setup is similar in spirit to light-shining-through-walls (LSW) experiments, but because the pump field itself effectively converts the ALP back to photons inside a single cavity, our sensitivity scales differently with the strength of the external fields, allowing for superior reach as compared to experiments like OSQAR while utilizing current technology. Furthermore, a well-defined program of increasing sensitivity has a guaranteed physics result: the first observation of the Euler-Heisenberg term of low-energy QED at energies below the electron mass. We discuss how the ALP contribution may be separated from the QED contribution by a suitable choice of pump modes and cavity geometry, and conclude by describing the ultimate sensitivity of our proposed program of experiments to ALPs.
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