So far, the observed effects of dark matter are compatible with it having purely gravitational interactions. However, in many models, dark matter has additional interactions with itself, with the Standard Model, and/or with additional hidden sector states. In this paper, we discuss models in which dark matter interacts through a light vector mediator, giving rise to a long-ranged force between dark matter particles. Coherent scattering effects through this force can lead to the exponential growth of small perturbations, in analogy to electromagnetic plasma instabilities. These instabilities can be significant at couplings many orders of magnitude below those for which the usual particle-by-particle constraints on dark matter self-interactions apply. While this possibility has been noted in the literature, we provide the first systematic study of such instabilities, including the case where the mediator has finite mass. The latter is relevant for models of kinetically mixed `dark photon' mediators, which represent an important target for proposed dark matter detection experiments. Our analyses are of the growth of small perturbations, so do not immediately provide observational constraints on dark matter models - however, they do motivate further study of large regions of parameter space.

中文翻译：

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长距离暗物质自相互作用和等离子体不稳定性

到目前为止，观察到的暗物质效应与它具有纯粹的引力相互作用是相容的。然而，在许多模型中，暗物质与自身、与标准模型和/或与其他隐藏扇区状态有额外的相互作用。在本文中，我们讨论了暗物质通过光矢量介体相互作用的模型，从而在暗物质粒子之间产生长程力。通过这种力的相干散射效应会导致小扰动的指数增长，类似于电磁等离子体的不稳定性。这些不稳定性在耦合比暗物质自相互作用的通常逐粒子约束适用的那些低许多数量级时可能很重要。虽然文献中已经提到了这种可能性，我们首次对这种不稳定性进行了系统研究，包括介体质量有限的情况。后者与动力学混合的“暗光子”介体模型相关，后者代表了暗物质探测实验的重要目标。我们的分析是关于小扰动的增长，因此不会立即对暗物质模型提供观测约束——然而，它们确实激发了对参数空间大区域的进一步研究。