The detection of a sterile neutrino could constitute the first observation of a particle that could have been produced before Big-Bang Nucleosynthesis (BBN), and could provide information about the yet untested pre-BBN era. The cosmological evolution in this era could be drastically different than typically assumed in what constitutes the standard cosmology, as happens in a variety of motivated particle models. In this work we assess the sensitivity to different pre-BBN cosmologies in which entropy is conserved of 0.01 eV to 1 MeV mass sterile neutrinos produced in the early Universe via resonant active-sterile oscillations, which requires a large lepton asymmetry. We identify mass ranges where it is possible to have two populations of the same sterile neutrino, one with a colder and one with a hotter momentum spectra, which is in principle an observable effect. Furthermore, we show the regions in mass and mixing where fully resonant production (i.e. simultaneously coherent and adiabatic) can occur. We find that in several of the cosmologies we consider, including the standard one, for a lepton asymmetry larger than $\sim10^{-4}$ fully resonantly produced sterile neutrinos in the eV-mass range can evade all cosmological constraints.

中文翻译：

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共振产生的无菌中微子的宇宙学依赖性

对惰性中微子的检测可能构成对可能在大爆炸核合成 (BBN) 之前产生的粒子的首次观察，并且可以提供有关尚未经过测试的前 BBN 时代的信息。这个时代的宇宙学演化可能与构成标准宇宙学的典型假设截然不同，就像在各种动机粒子模型中发生的那样。在这项工作中，我们评估了对不同的前 BBN 宇宙学的敏感性，其中熵守恒为 0.01 eV 到 1 MeV 质量的无菌中微子，通过共振活性无菌振荡在早期宇宙中产生，这需要大的轻子不对称性。我们确定了可能有两个相同惰性中微子群体的质量范围，一个具有更冷的动量谱，一个具有更热的动量谱，这原则上是一个可观察到的效果。此外，我们还展示了可以发生完全共振产生（即同时相干和绝热）的质量和混合区域。我们发现，在我们考虑的几种宇宙学中，包括标准宇宙学，对于大于 $\sim10^{-4}$ 的轻子不对称性，在 eV 质量范围内完全共振产生的无菌中微子可以逃避所有宇宙学约束。