We review the status of searches for sterile neutrinos in the $\sim 1$ eV range, with an emphasis on the latest results from short baseline oscillation experiments and how they fit within sterile neutrino oscillation models. We present global fit results to a three-active-flavor plus one-sterile-flavor model (3+1), where we find an improvement of $\Delta \chi^2=35$ for 3 additional parameters compared to a model with no sterile neutrino. This is a 5$\sigma$ improvement, indicating that an effect that is like that of a sterile neutrino is highly preferred by the data. However we note that separate fits to the appearance and disappearance oscillation data sets within a 3+1 model do not show the expected overlapping allowed regions in parameter space. This "tension" leads us to explore two options: 3+2, where a second additional mass state is introduced, and a 3+1+decay model, where the $\nu_4$ state can decay to invisible particles. The 3+1+decay model, which is also motivated by improving compatibility with cosmological observations, yields the larger improvement, with a $\Delta \chi^2=8$ for 1 additional parameter beyond the 3+1 model, which is a $2.6\sigma$ improvement. Moreover the tension between appearance and disappearance experiments is reduced compared to 3+1, although disagreement remains. In these studies, we use a frequentist approach and also a Bayesean method of finding credible regions. With respect to this tension, we review possible problems with the global fitting method. We note multiple issues, including problems with reproducing the experimental results, especially in the case of experiments that do not provide adequate data releases. We discuss an unexpected 5 MeV excess, observed in the reactor flux energy spectrum, that may be affecting the oscillation interpretation of the short baseline reactor data. We emphasize the care that must be taken in mapping to the true neutrino energy in the case of oscillation experiments that are subject to multiple interaction modes and nuclear effects. We point to problems with the "Parameter-Goodness-of-Fit test" that is used to quantify the tension. Lastly, we point out that analyses presenting limits often receive less scrutiny that signals. While we provide a snapshot of the status of sterile neutrino searches today and global fits to their interpretation, we emphasize that this is a fast-moving field. We briefly review experiments that are expected to report new data in the immediate future. Lastly, we consider the 5-year horizon, where we propose that decay-at-rest neutrino sources are the best method of finally resolving the confusing situation.

中文翻译：

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我们哪里有轻的无菌中微子？

我们回顾了在 $\sim 1$ eV 范围内搜索惰性中微子的状态，重点是短基线振荡实验的最新结果以及它们如何适应惰性中微子振荡模型。我们将全局拟合结果呈现给三种活性风味加一种无菌风味模型 (3+1)，与具有以下特征的模型相比，我们发现 3 个附加参数的 $\Delta \chi^2=35$ 改进没有无菌中微子。这是 5$\sigma$ 的改进，表明数据非常喜欢类似于无菌中微子的效果。然而，我们注意到，对 3+1 模型中出现和消失振荡数据集的单独拟合并未显示参数空间中预期的重叠允许区域。这种“张力”引导我们探索两种选择：3+2，其中引入了第二个附加质量状态，以及 3+1+衰减模型，其中 $\nu_4$ 状态可以衰减为不可见粒子。3+1+衰变模型也受到提高与宇宙学观测的兼容性的推动，产生了更大的改进，对于 3+1 模型之外的 1 个附加参数，$\Delta \chi^2=8$，这是一个$2.6\sigma$ 改进。此外，与 3+1 相比，出现和消失实验之间的紧张程度有所降低，尽管仍有分歧。在这些研究中，我们使用频率论方法和贝叶斯方法来寻找可信区域。关于这种张力，我们回顾了全局拟合方法可能存在的问题。我们注意到多个问题，包括重现实验结果的问题，特别是在没有提供足够数据发布的实验的情况下。我们讨论了在反应堆通量能谱中观察到的意外 5 MeV 过量，这可能会影响短基线反应堆数据的振荡解释。我们强调在受多种相互作用模式和核效应影响的振荡实验的情况下，映射到真正的中微子能量时必须小心。我们指出了用于量化张力的“参数拟合优度测试”的问题。最后，我们指出，呈现限制的分析通常会受到较少的审查。虽然我们提供了当今惰性中微子搜索状态的快照以及对其解释的全球拟合，但我们强调这是一个快速发展的领域。我们简要回顾了有望在不久的将来报告新数据的实验。最后，我们考虑 5 年的范围，我们建议静止衰变中微子源是最终解决混乱情况的最佳方法。