Abstract We present a simple model of two dark matter species with opposite millicharge that can form electrically neutral bound states via the exchange of a massive dark photon. If bound state formation is suppressed at low temperatures, a sub-dominant fraction of millicharged particles remains at late times, which can give rise to interesting features in the 21 cm absorption profile at cosmic dawn. The dominant neutral component, on the other hand, can have dipole interactions with ordinary matter, leading to non-standard signals in direct detection experiments. We identify the parameter regions predicting a percent-level ionisation fraction and study constraints from laboratory searches for dark matter scattering and dark photon decays.

中文翻译：

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在暗原子、大量暗光子和毫电荷子组件上

摘要 我们提出了两个具有相反毫电荷的暗物质物种的简单模型，它们可以通过大量暗光子的交换形成电中性束缚态。如果在低温下束缚态的形成受到抑制，则微带电粒子的次主导部分会保留在后期，这可能会在宇宙黎明时 21 厘米的吸收剖面中产生有趣的特征。另一方面，占主导地位的中性成分可以与普通物质发生偶极相互作用，导致直接检测实验中的非标准信号。我们确定了预测百分比水平电离分数的参数区域，并研究了实验室搜索暗物质散射和暗光子衰变的约束。