The origin and composition of the cosmological dark matter remain a mystery. However, upcoming 21-cm measurements during cosmic dawn, the period of the first stellar formation, can provide new clues on the nature of dark matter. During this era, the baryon-dark matter fluid is the slowest it will ever be, making it ideal to search for dark matter elastically scattering with baryons through massless mediators, such as the photon. Here we explore whether dark-matter particles with an electric “minicharge” can significantly alter the baryonic temperature and, thus, affect 21-cm observations. We find that the entirety of the dark matter cannot be minicharged at a significant level, lest it interferes with Galactic and extragalactic magnetic fields. However, if minicharged particles comprise a subpercent fraction of the dark matter, and have charges ∼ 10−6—in units of the electron charge—and masses mχ ∼ 1− 60 MeV, they can significantly cool down the baryonic fluid, and be discovered in 21-cm experiments. We show how this scenario can explain the recent result by the EDGES collaboration, which requires a lower baryonic temperature than possible within the standard model, while remaining consistent with all current observations.

中文翻译：

---

少量带微电的暗物质可以冷却早期宇宙的重子

宇宙学暗物质的起源和组成仍然是个谜。然而，即将在宇宙黎明（第一次恒星形成时期）进行的 21 厘米测量可以提供有关暗物质性质的新线索。在这个时代，重子-暗物质流体是有史以来最慢的，因此非常适合通过无质量介质（例如光子）搜索与重子弹性散射的暗物质。在这里，我们探讨了带有“微电荷”的暗物质粒子是否可以显着改变重子温度，从而影响 21 厘米的观测。我们发现整个暗物质不能在显着水平上微带电，以免干扰银河和河外磁场。然而，如果微带电粒子只占暗物质的一小部分，并且具有约 10−6 电荷（以电子电荷为单位）和质量 mx ∼ 1− 60 MeV，它们可以显着冷却重子流体，并在 21 厘米实验中被发现。我们展示了这种情况如何解释 EDGES 合作的最新结果，该结果需要比标准模型中可能的更低的重子温度，同时与所有当前观察结果保持一致。