arXiv 1209.57522012-09astro-ph.COhep-ph

原子暗物质的宇宙学

The Cosmology of Atomic Dark Matter

Francis-Yan Cyr-Racine, Kris Sigurdson

备注：: 32 pages + appendices, 24 figure. References added in v2
发表信息：: Phys. Rev. D 87, 103515 (2013)
DOI：: 10.1103/PhysRevD.87.103515

摘要：

然而，为了确保成功的宇宙学，暗物质（DM）必须在宇宙历史的早期从标准模型等离子体中运动学解耦，它可以保持耦合到“暗辐射”浴，直到相对较晚的时代。一个实现这种情况的最小理论是原子暗物质模型，其中两个费米子在新的U（1）暗力下带相反的电荷，最初耦合到“暗光子”的热浴中，但最终重新组合成中性原子状的束缚态，并开始形成引力束缚结构。由于暗原子具有（暗）原子大小的几何截面，该模型也提供了一个自相互作用DM与速度相关的截面的例子。在这种情况下，延迟动力学解耦预测新的DM性能在小尺度上，但保留了冷DM在较大尺度上的成功。我们计算所需的原子物理学捕捉这个黑暗的部门的热历史，并显示显着的改进，需要在标准的原子氢计算。我们解决了玻尔兹曼方程，在这个模型中的宇宙学波动的演变，并详细地发现原子DM方案上的物质功率谱和宇宙微波背景（CMB）的影响。这种情况下印记一个新的长度尺度，暗声振荡（DAO）规模，对物质密度场。这个DAO尺度塑造了小尺度物质的功率谱，并决定了后期最小的DM晕质量，这可能比典型的WIMP场景大很多个数量级。这个模型必然包括一个额外的黑暗辐射分量，这可能是目前的CMB实验的青睐，我们量化CMB签名区分原子DM方案从标准的$Λ$ CDM模型包含额外的自由流动粒子。[删节]

英文摘要：

While, to ensure successful cosmology, dark matter (DM) must kinematically decouple from the standard model plasma very early in the history of the Universe, it can remain coupled to a bath of "dark radiation" until a relatively late epoch. One minimal theory that realizes such a scenario is the Atomic Dark Matter model, in which two fermions oppositely charged under a new U(1) dark force are initially coupled to a thermal bath of "dark photons" but eventually recombine into neutral atom-like bound states and begin forming gravitationally-bound structures. As dark atoms have (dark) atom-sized geometric cross sections, this model also provides an example of self-interacting DM with a velocity-dependent cross section. Delayed kinetic decoupling in this scenario predicts novel DM properties on small scales but retains the success of cold DM on larger scales. We calculate the atomic physics necessary to capture the thermal history of this dark sector and show significant improvements over the standard atomic hydrogen calculation are needed. We solve the Boltzmann equations that govern the evolution of cosmological fluctuations in this model and find in detail the impact of the atomic DM scenario on the matter power spectrum and the cosmic microwave background (CMB). This scenario imprints a new length scale, the Dark-Acoustic-Oscillation (DAO) scale, on the matter density field. This DAO scale shapes the small-scale matter power spectrum and determines the minimal DM halo mass at late times which may be many orders of magnitude larger than in a typical WIMP scenario. This model necessarily includes an extra dark radiation component, which may be favoured by current CMB experiments, and we quantify CMB signatures that distinguish an atomic DM scenario from a standard $Λ$CDM model containing extra free-streaming particles. [Abridged]

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