Neutrinos, being the only fermions in the Standard Model of Particle Physics that do not possess electromagnetic or color charges, have the unique opportunity to communicate with fermions outside the Standard Model through mass mixing. Such Standard Model-singlet fermions are generally referred to as “sterile neutrinos”. In this review article, we discuss the theoretical and experimental motivation for sterile neutrinos, as well as their phenomenological consequences. With the benefit of hindsight in 2020, we point out potentially viable and interesting ideas. We focus in particular on sterile neutrinos that are light enough to participate in neutrino oscillations, but we also comment on the benefits of introducing heavier sterile states. We discuss the phenomenology of eV-scale sterile neutrinos in terrestrial experiments and in cosmology, we survey the global data, and we highlight various intriguing anomalies. We also expose the severe tension that exists between different data sets and prevents a consistent interpretation of the global data in at least the simplest sterile neutrino models. We discuss non-minimal scenarios that may alleviate some of this tension. We briefly review the status of keV-scale sterile neutrinos as dark matter and the possibility of explaining the matter–antimatter asymmetry of the Universe through leptogenesis driven by yet heavier sterile neutrinos.

中微子是粒子物理标准模型中唯一不具有电磁或色荷的费米子，具有独特的机会通过质量混合与标准模型之外的费米子进行通信。这种标准模型单线态费米子通常被称为“无菌中微子”。在这篇评论文章中，我们讨论了惰性中微子的理论和实验动机，以及它们的现象学后果。凭借 2020 年的后见之明，我们指出了潜在可行且有趣的想法。我们特别关注轻到足以参与中微子振荡的无菌中微子，但我们也评论了引入更重的无菌状态的好处。我们讨论了地球实验和宇宙​​学中 eV 级无菌中微子的现象学，我们调查了全球数据，并强调了各种有趣的异常现象。我们还暴露了不同数据集之间存在的严重张力，并且至少在最简单的惰性中微子模型中阻止了对全局数据的一致解释。我们讨论了可以缓解这种紧张局势的非最小场景。我们简要回顾了 keV 级惰性中微子作为暗物质的地位，以及通过更重的惰性中微子驱动的轻质发生来解释宇宙物质-反物质不对称的可能性。我们讨论了可以缓解这种紧张局势的非最小场景。我们简要回顾了 keV 级惰性中微子作为暗物质的地位，以及通过更重的惰性中微子驱动的轻质发生来解释宇宙物质-反物质不对称的可能性。我们讨论了可以缓解这种紧张局势的非最小场景。我们简要回顾了 keV 级惰性中微子作为暗物质的地位，以及通过更重的惰性中微子驱动的轻质发生来解释宇宙物质-反物质不对称的可能性。