包含原初黑洞遗迹的混合暗物质模型中的微调问题
Fine-tuning in mixed Dark Matter models with Primordial Black Hole relics
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中文总结 AI 辅助
该研究探讨含原初黑洞遗迹的混合暗物质模型的微调问题，分析不同暗物质产生机制与原初黑洞形成通道的参数敏感性，发现自然实现数量级为1的原初黑洞遗迹丰度较难。
中文摘要 AI 辅助
我们研究了三方暗物质（DM）场景的微调问题，该场景涉及超轻原初黑洞（PBHs），这些黑洞在大爆炸核合成之前蒸发，留下普朗克质量的遗迹，并产生DM粒子，同时还有独立产生的DM成分。我们均匀评估了再现观测到的DM丰度Ω_DM所需的参数灵敏度。考虑热WIMP冻结产生、冻结注入以及QCD轴子错位机制，并假设PBHs通过视界进入后的扰动坍缩形成，我们发现微调通常由PBH遗迹丰度计算的结构主导，而非粒子DM候选者或PBH蒸发的细节。在辐射主导的宇宙学中，DM丰度对原初曲率功率谱高度敏感，因为PBH形成分数依赖于密度涨落的指数。尽管早期PBH主导的时代会稀释预先存在的丰度并降低PBH丰度的表观微调，但仍需要暴胀微调来产生所需的初始大幅扰动。我们进一步研究了其他PBH形成通道，包括超冷一阶相变和坍缩畴壁，发现它们会用其他指数敏感性取代暴胀微调。我们得出结论，难以实现数量级为1的PBH遗迹丰度的自然实现。
英文摘要
We investigate the fine-tuning of a tripartite dark matter (DM) scenario involving ultra-light primordial black holes (PBHs), whose evaporation before Big Bang Nucleosynthesis leaves Planck-mass relics and produces DM particles together with an independently produced DM component. We uniformly evaluate the parameter sensitivity required to reproduce the observed DM abundance, $Ω_{\rm DM}$. Considering thermal WIMP freeze-out, freeze-in, and QCD axion misalignment, and assuming PBHs form via collapse of perturbations following horizon entry, we find that the fine-tuning is normally dominated by the structure of the PBH relic abundance calculation rather than by the particle DM candidate or the details of PBH evaporation. In radiation-dominated cosmologies, the DM abundance is highly sensitive to the primordial curvature power spectrum because the PBH formation fraction depends exponentially on density fluctuations. Although an early PBH-dominated era dilutes pre-existing abundances and reduces the apparent tuning of the PBH abundance, inflationary fine-tuning remains required to produce the required initial large amplitude perturbations. We further examine alternative PBH formation channels, including supercooled first-order phase transitions and collapsing domain walls, and find that they replace the inflationary fine-tuning with alternative exponential sensitivities. We conclude that a natural realization of an order unity PBH relic abundance is hard to motivate.
