逐步摆脱黑暗：通过时变混合从惰性中微子暗物质到中微子质量
Phasing out of Darkness: From Sterile Neutrino Dark Matter to Neutrino Masses via Time-Dependent Mixing
AI总结：
本研究提出含两个右手中微子与辅助标量场的时变模型，通过晚近仍在进行的相变调控活性-惰性混合，规避X射线约束，同时解释暗物质与中微子质量，且预言可被未来实验检验。
摘要：
惰性中微子是产生中微子质量、阐明暗物质本质的极具潜力的候选粒子。然而，天体物理X射线观测对惰性中微子暗物质衰变的约束，在很大程度上排除了I型跷跷板框架下同时产生正确的左手中微子能谱与keV量级右手中微子暗物质所需的活性-惰性混合。本研究中，我们论证了如何通过一种时变方法规避这些X射线约束，从而使大范围的活性-惰性混合方案重新具备可行性。我们的最简模型包含两个右手中微子（构成双组分暗物质候选体），以及一个辅助标量场——该标量场经历了极晚且仍在进行的相变，导致全局$U(1)_N$对称性自发破缺。在此次相变发生前，只有右手中微子具有质量，左手中微子因标量场的真空期望值为零而保持无质量。随着相变推进，标量场不断增大的真空期望值提升了活性-惰性混合程度，由此开启暗物质衰变通道并诱导产生中微子质量。这种时间相关性使得该方案既符合X射线约束，也与当前左手中微子质量的测量结果一致。目前预期的活性-惰性混合水平处于即将开展的TRISTAN（KATRIN）氚β衰变项目的探测能力范围内。此外，DESI、EUCLID等宇宙学巡天以及超新星中微子观测可检验相变前左手中微子无质量的预言。
英文摘要：
Sterile neutrinos are a compelling candidate for generating neutrino masses and for elucidating the nature of dark matter. Astrophysical X-ray constraints on sterile neutrino dark matter decays, however, largely exclude the active-sterile mixing required to produce simultaneously the correct left-handed neutrino spectrum and keV-scale right-handed neutrino dark matter within a type-I seesaw framework. In this study, we demonstrate how these X-ray constraints can be circumvented through a time-dependent approach, thereby reviving a broad range of active-sterile mixing scenarios. Our minimal model incorporates two right-handed neutrinos, which form a two-component dark matter candidate, and an auxiliary scalar field that experiences a very late and still ongoing phase transition, leading to the spontaneous breaking of a global $ U(1)_N $ symmetry. Prior to this phase transition, only the right-handed neutrinos are massive, while the left-handed neutrinos remain massless because of the scalar field's vanishing expectation value. As the phase transition develops, the growing expectation value of the scalar field increases the active-sterile mixing, thereby opening dark matter decay channels and inducing neutrino masses. The time dependence allows the scenario to be consistent with X-ray constraints as well as current measurements of left-handed neutrino masses. The anticipated level of active-sterile mixing today is within the detection capabilities of the forthcoming TRISTAN (KATRIN) tritium-beta decay project. Additionally, cosmological surveys such as DESI or EUCLID and supernova neutrino observations can test the prediction of massless left-handed neutrinos prior to the phase transition.
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