arXiv 1207.31242012-07-13astro-ph.CO

作为冷暗物质候选者的轴子：低质量情况

Axion as a cold dark matter candidate: low-mass case

Chan-Gyung Park, Jai-chan Hwang, Hyerim Noh

备注：: 9 pages, 8 figures
DOI：: 10.1103/PhysRevD.86.083535

摘要：

作为相干振荡标量场的轴子在所有宇宙学相关尺度下都表现为冷暗物质。对于质量为10^{-5} eV的常规轴子，在小于太阳系尺度的密度扰动演化中，轴子表现出特征阻尼行为。阻尼尺度与轴子质量的平方根成反比。我们发现，小于10^{-24} eV的轴子质量在宇宙学相关尺度中引起重子密度功率谱的显著阻尼，从而在小于轴子金斯尺度的尺度中偏离冷暗物质。然而，由于质量如此之小，我们关于相干振荡的标量场的基本假设在早期宇宙中被打破了。基于玻色-爱因斯坦凝聚体和超轻标量场的其他暗物质模型也存在这个问题。我们引入一个简单的模型，以避免这个问题，在早期宇宙中引入演化的轴子质量，目前的低质量轴子的重子密度功率谱，宇宙微波背景辐射（CMB）的温度功率谱，和重子密度扰动的增长率的观测效果。在我们的低质量轴子模型中，我们有一个特征性的小尺度截断的重子密度功率谱低于轴子金斯尺度。在物质和CMB功率谱中，与冷暗物质模型的小尺度偏差明显不同于在冷暗物质模型中与作为热暗物质组分的大质量中微子混合的预期偏差。

英文摘要：

Axion as a coherently oscillating scalar field is known to behave as a cold dark matter in all cosmologically relevant scales. For conventional axion mass with 10^{-5} eV, the axion reveals a characteristic damping behavior in the evolution of density perturbations on scales smaller than the solar system size. The damping scale is inversely proportional to the square-root of the axion mass. We show that the axion mass smaller than 10^{-24} eV induces a significant damping in the baryonic density power spectrum in cosmologically relevant scales, thus deviating from the cold dark matter in the scale smaller than the axion Jeans scale. With such a small mass, however, our basic assumption about the coherently oscillating scalar field is broken in the early universe. This problem is shared by other dark matter models based on the Bose-Einstein condensate and the ultra-light scalar field. We introduce a simple model to avoid this problem by introducing evolving axion mass in the early universe, and present observational effects of present-day low-mass axion on the baryon density power spectrum, the cosmic microwave background radiation (CMB) temperature power spectrum, and the growth rate of baryon density perturbation. In our low-mass axion model we have a characteristic small-scale cutoff in the baryon density power spectrum below the axion Jeans scale. The small-scale deviations from the cold dark matter model in both matter and CMB power spectra clearly differ from the ones expected in the cold dark matter model mixed with the massive neutrinos as a hot dark matter component.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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英文摘要：

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