Possible interactions of dark matter (DM) with Standard Model (SM) particles can be tested with spectral distortions (SDs) of the cosmic microwave background (CMB). In particular, a nonrelativistic DM particle that scatters elastically with photons, electrons, or nuclei imprints a negative chemical potential $\mu$ to the CMB spectrum. This article revisits the first study of this effect, with an accurate treatment of heat exchange between DM and SM particles. We show that the instantaneous-decoupling approximation made in the original study systematically and significantly underestimates the amplitude of SDs. As a consequence, we derive tighter upper bounds to the DM-SM elastic-scattering cross section for DM masses $m_{\chi }\lesssim 0.1\mathrm{MeV}$, from the nondetection of $\mu$-distortions by FIRAS. We also show that a future instrument like PIXIE, sensitive to $|\mu |\sim {10}^{-8}$, would be able to probe DM-SM cross sections much smaller than first forecasted, and orders of magnitude below current upper limits from CMB-anisotropy data, up to DM masses of $\sim 1\mathrm{GeV}$. Lastly, we study the sensitivity of SDs to the electric and magnetic dipole moments of the DM. Although SDs can place nontrivial constraints on these models, we find that even future SD experiments are unlikely to improve upon the best current bounds. This article is accompanied by the public code dmdist, which allows one to compute CMB SDs for generic particle-DM models, specified by their cross sections for elastic scattering with and annihilation into SM particles.

中文翻译：

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测试具有CMB光谱失真的暗物质相互作用

暗物质（DM）与标准模型（SM）粒子的可能相互作用可以通过宇宙微波背景（CMB）的光谱畸变（SD）进行测试。特别是，非相对论的DM粒子与光子，电子或原子核弹性散射会产生负的化学势$\mu$到CMB频谱。本文通过对DM和SM颗粒之间的热交换进行精确处理，回顾了对此效应的首次研究。我们表明，原始研究中的瞬时解耦近似系统地并且大大低估了SD的幅度。结果，我们得出了DM质量的DM-SM弹性散射截面的更严格的上限${米}_{\chi }\lesssim 0.1\mathrm{电动汽车}$，来自未检测到 $\mu$-由FIRAS造成的失真。我们还表明，像PIXIE这样的未来仪器对$|\mu |〜{10}^{-8}$能够探测到比最初预测的要小得多的DM-SM横截面，并且比CMB各向异性数据的当前上限低几个数量级，直到DM质量达到 $〜\mathrm{1个}\mathrm{GeV}$。最后，我们研究了SD对DM的电和磁偶极矩的敏感性。尽管SD可以对这些模型施加非平凡的约束，但我们发现，即使未来的SD实验也无法在最佳当前范围上进行改进。本文随附了公共代码dmdist，该代码允许使用dmdist计算通用粒子DM模型的CMB SD，该模型由其横截面指定，用于随着SM粒子的弹性散射和and灭。