Photons traveling cosmological distances through the inhomogeneous Universe experience a great variation in their in-medium induced effective mass. Using the EAGLE suite of hydrodynamical simulations, we infer the free electron distribution and thereby the effective photon mass after reionization. We use this data to study the inter-conversion of kinetically mixed photons and dark photons, which may occur at a great number of resonance redshifts, and obtain the "optical depth" against conversion along random lines-of-sight. Using COBE/FIRAS, Planck, and SPT measurements, we constrain the dark photon parameter space from the depletion of CMB photons into dark photons that causes both spectral distortions and additional anisotropies in the CMB. Finally, we also consider the conversion of sub-eV dark radiation into ordinary photons. We make the line-of-sight distributions of both, free electrons and dark matter, publicly available.

中文翻译：

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非均匀宇宙中的有效光子质量和（暗）光子转换

在非均匀宇宙中传播宇宙学距离的光子经历了它们在介质中诱导的有效质量的巨大变化。使用 EAGLE 流体动力学模拟套件，我们推断自由电子分布，从而推断再电离后的有效光子质量。我们使用这些数据来研究动力学混合光子和暗光子的相互转换，这可能发生在大量共振红移处，并获得沿随机视线转换的“光学深度”。使用 COBE/FIRAS、普朗克和 SPT 测量，我们将暗光子参数空间从 CMB 光子的消耗限制为暗光子，这会导致 CMB 中的光谱失真和其他各向异性。最后，我们还考虑了 sub-eV 暗辐射到普通光子的转换。