标题： 冷暗物质微晕的密度分布及其对湮灭增强因子的影响 显示英文标题

标题： Density Profiles of CDM Microhalos and their Implications for Annihilation Boost Factors

摘要： 在一个标准的冷暗物质（CDM）宇宙学中，处在CDM截止尺度上的微晕是预期在宇宙中首先形成且最小的结构。 在这里我们展示了三个具有代表性的、接近地球质量的微晕高分辨率模拟结果，以确定它们的内部密度分布。 我们发现，在功率谱没有截止的CDM模拟中，这些微晕的内部密度分布大致遵循NFW密度分布，就像在星系和星系团尺度上大得多的CDM晕一样。 但是，如果初始功率谱在典型的中性子自由流尺度（$10^{-7} M_{\odot}$）上有截止，则它们的内部密度分布会变得明显更陡峭，即$\rho \propto r^{-(1.3-1.4)}$，这与石山等人（2010年）的结果非常一致。 将晕质量和亚晕质量函数外推到截止尺度表明，微晕在整个当前的暗物质分布中极为丰富，并可能对间接探测暗物质信号做出显著贡献。 假设从NFW分布过渡到一个更陡峭的内部分布（$\rho \propto r^{-1.4}$），比截止尺度高出两个数量级，则一个类似银河系大小的暗物质晕的总增强因子将从约3.5增加到4。 我们进一步发现，CDM微晕的集中度与Bullock等人（2001年）的模型一致，并明确排除了关于集中度和亚晕湮灭质量依赖关系的简单幂律模型，因为这种模型会导致错误的非常大的增强因子（对于星系晕约为几百，对于星系团超过1000）。 显示英文摘要

摘要： In a standard cold dark matter (CDM) cosmology, microhalos at the CDM cutoff scale are the first and smallest objects expected to form in the universe. Here we present results of high resolution simulations of three representative roughly Earth-mass microhalos in order to determine their inner density profile. We find that CDM microhalos in simulations without a cutoff in the power spectrum roughly follow the NFW density profile, just like the much larger CDM halos on galaxy and galaxy cluster scales. But having a cutoff in the initial power spectrum at a typical neutralino free streaming scale of $10^{-7} M_{\odot}$ makes their inner density profiles considerably steeper, i.e. $\rho \propto r^{-(1.3-1.4)}$, in good agreement with the results from Ishiyama et al. (2010). An extrapolation of the halo and subhalo mass functions down to the cutoff scale indicates that microhalos are extremely abundant throughout the present day dark matter distribution and might contribute significantly to indirect dark matter detection signals. Assuming a transition from a NFW to a steeper inner profile ($\rho \propto r^{-1.4}$) two orders of magnitude above the cutoff scale, the total boost factor for a Milky Way sized dark matter halo increases from about 3.5 to 4. We further find that CDM microhalo concentrations are consistent with the Bullock et al. (2001) model and clearly rule out simplistic power law models for the mass dependence of concentrations and subhalo annihilation, which would erroneously lead to very large boost factors (a few hundred for galaxy halos and over 1000 for clusters).