得到了大量的虚无：宇宙空洞作为粒子暗物质的探针
Got plenty of nothing: cosmic voids as a probe of particle dark matter
摘要：
根据暗物质湮灭或衰变产生的辐射来寻找粒子暗物质信号，必须应对预测信号的极端微弱和掩蔽天体物理背景的存在。它已被证明，使用宇宙中的暗物质分布与宇宙辐射场的波动之间的相关信息，有可能允许设置从天体物理发射的纯暗物质信号，因为空间波动的辐射场由于天体物理源和暗物质发射有不同的功能。互相关技术已被提出并通过观察暗物质晕（过密度）用于暗物质研究。在本文中，我们通过关注宇宙空洞提供的暗物质分布信息，并通过专门研究伽马射线暗物质发射来扩展该技术：我们表明，虽然是欠密度的，因此与晕相比产生减少的发射，但是在空隙中由于衰减的暗物质与天体物理源的互相关信号的相对大小明显更有利，对于高达$2 \times 10^{30}$ s的衰变寿命，产生大于1的信号背景比$S/B$（甚至显著地）。这与晕圈的情况不同，其中$S/B$通常（甚至远）小于1。我们表明，即将到来的星系调查，如欧几里得与未来一代的伽马射线探测器与改进的规格相结合，有能力提供这样的信号与预测的意义高达$5.7σ$的星系和$1.6σ$的宇宙剪切的提示。利用空隙可达到的暗物质寿命上的约束，预计将改善当前的约束在质量范围为$25\div900$ GeV的WIMP。
英文摘要：
The search for a particle dark matter signal in terms of radiation produced by dark matter annihilation or decay has to cope with the extreme faintness of the predicted signal and the presence of masking astrophysical backgrounds. It has been shown that using the correlated information between the dark matter distribution in the Universe with the fluctuations of the cosmic radiation fields has the potential to allow setting apart a pure dark matter signal from astrophysical emissions, since spatial fluctuations in the radiation field due to astrophysical sources and dark matter emission have different features. The cross-correlation technique has been proposed and adopted for dark matter studies by looking at dark matter halos (overdensities). In this paper we extend the technique by focusing on the information on dark matter distribution offered by cosmic voids, and by looking specifically at the gamma-ray dark matter emission: we show that, while being underdense and therefore producing a reduced emission as compared to halos, nevertheless in voids the relative size of the cross-correlation signal due to decaying dark matter vs. astrophysical sources is significantly more favourable, producing signal-to-background ratios $S/B$ (even significantly) larger than 1 for decay lifetimes up to $2 \times 10^{30}$ s. This is at variance with the case of halos, where $S/B$ is typically (even much) smaller than 1. We show that forthcoming galaxy surveys such as Euclid combined with future generation gamma-ray detectors with improved specifications have the ability to provide a hint of such a signal with a predicted significance up to $5.7σ$ for galaxies and $1.6σ$ for the cosmic shear. The bound on the dark matter lifetime attainable exploiting voids is predicted to improve on current bounds in a mass range for the WIMP of $25\div900$ GeV.
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