Traditional direct searches for dark matter, looking for nuclear recoils in deep underground detectors, are challenged by an almost complete loss of sensitivity for light dark matter particles. Consequently, there is a significant effort in the community to devise new methods and experiments to overcome these difficulties, constantly pushing the limits of the lowest dark matter mass that can be probed this way. From a model-building perspective, the scattering of sub-GeV dark matter on nucleons essentially must proceed via new light mediator particles, given that collider searches place extremely stringent bounds on contact-type interactions. Here we present an updated compilation of relevant limits for the case of a scalar mediator, including a new estimate of the near-future sensitivity of the NA62 experiment as well as a detailed evaluation of the model-specific limits from Big Bang nucleosynthesis. We also derive updated and more general limits on DM particles upscattered by cosmic rays, applicable to arbitrary energy- and momentum dependences of the scattering cross section. Finally we stress that dark matter self-interactions, when evaluated beyond the common s -wave approximation, place stringent limits independently of the dark matter production mechanism. These are, for the relevant parameter space, generically comparable to those that apply in the commonly studied freeze-out case. We conclude that the combination of existing (or expected) constraints from accelerators and astrophysics, combined with cosmological requirements, puts robust limits on the maximally possible nuclear scattering rate. In most regions of parameter space these are at least competitive with the best projected limits from currently planned direct detection experiments.

中文翻译：

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亚GeV暗物质的直接检测和互补约束

传统的暗物质直接搜索，即在地下深处探测器中寻找核反冲，面临着对轻暗物质粒子几乎完全丧失灵敏度的挑战。因此，社区付出了巨大的努力来设计新的方法和实验来克服这些困难，不断推动可以通过这种方式探测的最低暗物质质量的极限。从模型构建的角度来看，考虑到对撞机搜索对接触型相互作用施加了极其严格的限制，亚 GeV 暗物质在核子上的散射基本上必须通过新的光介体粒子进行。在这里，我们针对标量介体的情况提供了相关限制的更新汇编，包括对 NA62 实验近期灵敏度的新估计以及对大爆炸核合成模型特定限制的详细评估。我们还推导出了对宇宙射线向上散射的 DM 粒子的更新和更一般的限制，适用于散射截面的任意能量和动量依赖性。最后，我们强调暗物质自相互作用，当评估超出常见的 s 波近似值时，严格限制独立于暗物质产生机制。对于相关参数空间，这些通常与适用于普遍研究的冻结情况的那些参数相当。我们得出结论，来自加速器和天体物理学的现有（或预期）约束与宇宙学要求相结合，对最大可能的核散射率施加了严格的限制。在参数空间的大多数区域中，这些至少与当前计划的直接检测实验中的最佳预测限制具有竞争力。