发表机构
Institute for Nuclear Research of the Russian Academy of Sciences; Moscow Institute of Physics and Technology（俄罗斯科学院核物理研究所; 莫斯科物理技术学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文发现高轻子味不对称性会延迟惰性中微子共振产生并触发活性中微子振荡，从而自然饱和暗物质丰度，并给出混合参数的两个数量级约束范围。
AI 中文摘要
惰性中微子仍然是一个有充分动机的暗物质候选者，其宇宙学丰度可以通过在原始等离子体中存在轻子不对称性时的共振活性-惰性转换来增强。在标准图像中，更大的初始不对称性会增加物质势，因此可以促进共振产生。然而，同样的增加也会将共振转移到宇宙学演化的后期阶段，此时等离子体温度较低。我们表明，这种延迟的产生时期可能与活性中微子振荡的开始重叠，活性中微子振荡会重新分配味不对称性，并可能大幅减少，或在某些情况下几乎消除，成功共振惰性中微子产生所需的轻子不对称性。这种相互作用为最终惰性中微子丰度提供了一种自然饱和机制：超过一定的初始不对称性范围，增加原始不对称性不再导致产生的暗物质密度成比例增加。我们将此效应识别为在大轻子不对称性下共振惰性中微子产生的额外约束，并讨论其对初始不对称性的味结构和背景宇宙学演化的依赖性。我们的数值结果揭示了目前与暗物质惰性中微子产生共振机制一致的惰性-活性中微子混合参数$\sin^2(2\theta)$存在两个数量级的范围。必须由下一代X射线望远镜进行研究，以充分探索这一机制和相应的最小模型，这些模型表明惰性中微子作为可行的暗物质。我们还考虑了大味轻子不对称性下的π介子凝聚，这可能导致早期宇宙中的一阶QCD相变和相关的引力波产生。
英文摘要
Sterile neutrinos remain a well-motivated dark-matter candidate whose cosmological abundance can be enhanced by resonant active--sterile conversion in the presence of a lepton asymmetry in primordial plasma. In the standard picture, a larger initial asymmetry increases the matter potential and can therefore promote resonant production. However, the same increase also shifts the resonance to later stages of the cosmological evolution when the plasma temperature is lower. We show that this delayed production epoch can overlap with the onset of active neutrino oscillations, which redistribute the flavor asymmetries and may substantially reduce, or in some cases nearly erase, the lepton asymmetry needed for a successful resonant sterile-neutrino production. This interplay provides a natural saturation mechanism for the final sterile-neutrino abundance: beyond a certain range of initial asymmetries, increasing the primordial asymmetry no longer leads to a proportional increase in the produced dark-matter density. We identify this effect as an additional constraint on resonant sterile-neutrino production at large lepton asymmetry and discuss its dependence on the flavor structure of the initial asymmetry and on the background cosmological evolution. Our numerical results reveal two order of magnitude range in sterile-active neutrino mixing parameter $\sin^2(2θ)$ presently consistent with the resonant mechanism of the dark matter sterile neutrino production. It must be investigated by the next generation X-ray telescopes to fully explore this mechanism and corresponding minimal models suggesting sterile neutrinos as viable dark matter. We also consider pion condensation at large flavor lepton asymmetries, which may lead to a first-order QCD phase transition and associated gravitational-wave production in the early Universe.
Comments23 pages, 8 figures
