发表机构
Korea Institute for Advanced Study; Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences (HIAS-UCAS); Department of Physics, Kyungpook National University; Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS)（韩国高等科学研究院; 中国科学院大学杭州高等研究院; 庆北国立大学物理系; 基础科学研究所宇宙理论物理中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究提出一种惰性 sector 内的共振产生机制，通过N₁-N₂相干转换等产生自相互作用惰性中微子冷暗物质，无需显著活性-惰性混合，其丰度与N₁质量近似无关。
AI 中文摘要
惰性中微子是极具潜力的暗物质候选体，但它们通过活性-惰性中微子混合的传统产生机制受到X射线探测和结构形成观测的严格限制。我们提出一种完全在惰性 sector 内运作的独特产生机制：两个惰性中微子N₁和N₂，它们与一个单态标量φ耦合，其中N₁为暗物质候选体，N₂通过其标量相互作用诱导的频繁散射保持热平衡。由N₂和φ背景诱导的热自能会产生温度相关的质量分裂，以及N₁和N₂之间的非对角混合。随着宇宙冷却，介质中的能级可能发生能级交叉，导致热N₂粒子群向N₁的共振增强转换。我们采用密度矩阵动力学方程来描述该转换，该方程一致地包含了N₁-N₂的相干转换、碰撞退相干以及N₂的热再产生。对于窄共振，尽管存在碰撞阻尼动力学，积分转换概率仍具有与朗道-齐纳结果一致的简单解析形式。在与冻入（freeze-in）相关的弱转换 regime 中，这种对应关系为共振产生提供了可靠的解析描述。我们推导了由此产生的暗物质丰度，并确定了N₁的宇宙学稳定性条件，以及共振转换主导直接散射和衰变产生的条件。所得的遗迹丰度标度为Y₁∝g₁₂²g₂₂M_Pl/m₁，使得暗物质能量密度近似与m₁无关。该机制为惰性中微子暗物质提供了一条新途径，无需显著的活性-惰性中微子混合。
英文摘要
Sterile neutrinos are well-motivated dark matter candidates, but their conventional production through active-sterile mixing is tightly constrained by X-ray searches and structure-formation observations. We propose a distinct production mechanism operating entirely within a sterile sector: two sterile neutrinos, $N_1$ and $N_2$, coupled to a singlet scalar $ϕ$, with $N_1$ the dark matter candidate and $N_2$ held in equilibrium through frequent scattering induced by its scalar interaction. Thermal self-energies induced by the $N_2$ and $ϕ$ backgrounds generate both a temperature-dependent mass splitting and an off-diagonal mixing between $N_1$ and $N_2$. As the Universe cools, the in-medium levels can undergo a level crossing, leading to resonantly enhanced conversion of the thermal $N_2$ population into $N_1$. We formulate the conversion using a density-matrix kinetic equation that consistently incorporates coherent $N_1$-$N_2$ conversion, collisional decoherence, and thermal repopulation of $N_2$. For a narrow resonance, the integrated conversion probability admits a simple analytic form that coincides with the Landau-Zener result, despite the underlying collisionally damped dynamics. In the weak-conversion regime relevant for freeze-in, this correspondence provides a robust analytic description of the resonant production. We derive the resulting dark matter abundance and identify the conditions for cosmological stability of $N_1$ and for resonant conversion to dominate over direct scattering and decay production. The resulting relic abundance scales as $Y_1\propto g_{12}^2 g_{22}M_{\rm Pl}/m_1$, making the dark matter energy density approximately independent of $m_1$. This mechanism provides a new route to sterile-neutrino dark matter that does not require appreciable active-sterile mixing.
Comments21 pages, 1 figure, comments are welcome
