来自暗物质自旋翻转相互作用的强宽带21厘米宇宙学信号
A strong broadband 21 cm cosmological signal from dark matter spin-flip interactions
AI总结：
本文提出暗物质经轻轴矢媒介与电子发生自旋翻转相互作用，可产生从1.4 MHz延伸至恒星形成频段的强宽带21厘米吸收信号，并指出未来短程自旋力实验可检验该媒介粒子。
摘要：
在标准宇宙学中，人们认为全局宇宙学21厘米信号中存在两个相对较弱且彼此不同的带限吸收特征：第一个吸收极小值位于20 MHz附近（z∼70），另一个极小值位于50–110 MHz之间的较高频率（z∼12–27）；它们分别是宇宙黑暗时代碰撞气体动力学以及宇宙黎明时期第一代恒星所产生Lyman-α光子的标志。在具有额外气体冷却的模型中，也预期会有类似的两个不同带限但更强的吸收特征，这类模型曾被用来解释EDGES信号。在本工作中，我们探索一种新机制：暗物质通过轻质量轴矢媒介粒子与电子发生自旋翻转相互作用，可直接诱发21厘米吸收信号，其特征与上述两类信号均不同。我们普遍发现，我们的模型预言一个强的宽带吸收信号，从低至1.4 MHz（z∼1000）的频率——即宇宙黑暗时代早期，此时并不预期存在常规信号——一直延伸到恒星形成和X射线加热效应预期会终止吸收信号的较高频率。在标准宇宙学和额外气体冷却模型中，预期由吸收信号推断出的气体自旋温度是气体动力学温度的示踪物。然而，在我们的模型中，我们发现在参数空间的某些区域，气体的自旋温度和动力学温度以不同方式演化，而吸收信号只测量自旋温度的演化。我们所关注模型参数空间的大片区域不受现有约束限制，但未来在毫米到纳米尺度上寻找电子之间短程自旋相关作用力的实验，有可能发现导致我们所预言信号的轻质量媒介粒子。
英文摘要：
In the standard cosmology, it is believed that there are two relatively weak and distinct band-limited absorption features, with the first absorption minima near 20 MHz ($z\sim70$) and the other minima at higher frequencies between 50-110 MHz ($z\sim12-27$) in the global cosmological 21cm signal, which are signatures of collisional gas dynamics in the cosmic dark ages and Lyman-$α$ photons from the first stars at cosmic dawn, respectively. A similar prediction of two distinct band-limited, but stronger, absorption features is expected in models with excess gas cooling, which have been invoked to explain the EDGES signal. In this work, we explore a novel mechanism, where dark matter spin-flip interactions with electrons through a light axial-vector mediator could directly induce a 21cm absorption signal which is characteristically different from either of these. We find generically, that our model predicts a strong, broadband absorption signal extending from frequencies as low as 1.4 MHz ($z\sim1000$), from early in the cosmic dark ages where no conventional signal is expected, all the way up to higher frequencies where star formation and X-ray heating effects are expected to terminate the absorption signal. In the standard cosmology and in excess gas cooling models it is expected that the gas spin temperature as inferred from the absorption signal is a tracer of the gas kinetic temperature. However, in our model we find in certain regions of parameter space that the spin temperature and kinetic temperature of the gas evolve differently, and the absorption signal only measures the spin temperature evolution. Large swathes of our model parameter space of interest are safe from existing constraints, however future searches for short range spin-dependent forces between electrons on the mm to nm scale have the potential to discover the light mediator responsible for our predicted signal.
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