Primordial scalar and tensor modes can induce Cosmic Microwave Background spectral distortions during horizon re-entry. We investigate a specific mechanism proposed for this purpose, characterized by the coupling of an SU(2) gauge field to an axion undergoing a momentary stage of rapid evolution during inflation. Examining in details the perturbations produced by this model, we find that spectral distortions from the scalar modes significantly dominate those arising from the tensors. This holds true also for an earlier version of the model based on a U(1) gauge field. The scalar-induced distortions might be observed in future experiments, and the current COBE/FIRAS constraints already limit the parameter space of these models. Additionally, we find that delaying the onset of fast roll in the SU(2) scenario (to enhance the modes at the scales relevant for spectral distortions, while respecting the CMB constraints at larger scales) poses a greater challenge compared to the U(1) case. We propose a way to control the axion speed by varying the size of its coupling to the gauge fields.

中文翻译：

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增强的原始扰动导致的 CMB 光谱畸变：观察者轴子的作用


原初标量和张量模式会在地平线再入期间引起宇宙微波背景光谱畸变。我们研究了为此目的提出的一种特定机制，其特点是 SU(2) 规范场与轴子的耦合，轴子在暴胀过程中经历短暂的快速演化阶段。详细检查该模型产生的扰动，我们发现标量模式的谱畸变显着主导着张量产生的扰动。这也适用于基于 U(1) 规范场的模型的早期版本。在未来的实验中可能会观察到标量引起的畸变，并且当前的 COBE/FIRAS 约束已经限制了这些模型的参数空间。此外，我们发现，与 U(1) 场景相比，延迟 SU(2) 场景中快速滚转的开始（以增强与光谱失真相关的尺度上的模式，同时尊重更大尺度上的 CMB 约束）带来了更大的挑战） 案件。我们提出了一种通过改变轴子与规范场耦合的大小来控制轴子速度的方法。