探索暗原子的天体物理学
Exploring the astrophysics of dark atoms
摘要：
暗物质的一个组成部分可能由两个具有大质量比的暗带电粒子和一个无质量的力载体组成。这个“原子”暗区的行为可能与重子暗区非常相似，冷却并分裂成恒星质量或更小的尺度。过去的研究表明，宇宙微波背景和大尺度结构的限制排除了暗物质的$\gtrsim 5\%$以这种方式行为。然而，我们表明，即使百分之一级的质量分数，一个黑暗的原子部门可能会影响一些河外和银河系的观测。我们跟踪冷却和合并的历史原子暗组件的大部分有趣的参数空间。与重子不同，恒星反馈（由核物理驱动）延迟了星系的形成和生长，冷却暗原子气体通常会导致盘形成更早，留下更多的时间通过合并摧毁它们。而不是盘在银河系大小的晕，我们发现，最终产品是典型的星系尺度上的球状结构或暗原子碎片分布在晕尺度。这一结果与之前的研究形成了鲜明对比，之前的研究假设暗原子会导致暗盘。此外，暗原子凝聚成致密的团块，类似于太阳质量尺度上的重子碎片。我们估计这些黑暗的团块的大小，并使用这些估计表明，可行的原子暗物质参数空间被排除由恒星微透镜，由超微弱矮星系的半光半径，并通过银河系质量到光的推论。
英文摘要：
A component of the dark matter could consist of two darkly charged particles with a large mass ratio and a massless force carrier. This `atomic' dark sector could behave much like the baryonic sector, cooling and fragmenting down to stellar-mass or smaller scales. Past studies have shown that cosmic microwave background and large-scale structure constraints rule out $\gtrsim 5\%$ of the dark matter to behave in this manner. However, we show that, even with percent level mass fractions, a dark atomic sector could affect some extragalactic and galactic observables. We track the cooling and merger history of an atomic dark component for much of the interesting parameter space. Unlike the baryons, where stellar feedback (driven by nuclear physics) delays the formation and growth of galaxies, cooling dark atomic gas typically results in disks forming earlier, leaving more time for their destruction via mergers. Rather than disks in Milky Way sized halos, we find the end product is typically spheroidal structures on galactic scales or dark atom fragments distributed on halo scales. This result contrasts with previous studies, which had assumed that the dark atoms would result in dark disks. Furthermore the dark atoms condense into dense clumps, analogous to how the baryons fragment on solar-mass scales. We estimate the size of these dark clumps, and use these estimates to show that viable atomic dark matter parameter space is ruled out by stellar microlensing, by the half-light radii of ultra-faint dwarf galaxies, and by Milky Way mass-to-light inferences.
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