论文标题
宇宙学中中微子相互作用的全球视图：普朗克所见的自由式窗口
Global view of neutrino interactions in cosmology: The freestreaming window as seen by Planck
论文作者
论文摘要
中微子有望在温度下在早期的宇宙中在早期的宇宙中脱离$ t \ sim 2〜 {\ rm mev} $，因此中微子将在早期的宇宙中脱离。但是，有许多相关的粒子物理场景可以使中微子以$ t <2〜 {\ rm mev} $相互作用。在这项工作中，我们采用全球视角，旨在确定中微子可以在当前的宇宙学观察中相互作用的温度范围。我们考虑一组通用的速率参数化中微子相互作用，并通过执行完整的Planck宇宙微波背景（CMB）分析，我们发现中微子无法显着相互作用，而红移$ 2000 \ sillesim z \ Lessim z \ Lessim 10^5 $，我们将其称为自由播放窗口。我们还通过适当定义的交互速率$γ_\ text {nfs}（z）$得出了红移依赖的上限，找到$γ_\ text {nfs}（z）/h（z）/h（z）\ Lessim 1-10 $ 1-10 $。我们表明，这些结果在某些广泛的假设下在很大程度上独立于模型，并在中微子衰减，中微子自我互动，中微子歼灭和Maparon模型方面将它们与背景相关。我们提供了如何使用独立模型的方法在特定情况下获得界限的示例，并证明了与现有结果的一致性。我们还研究了即将到来的宇宙学数据的范围，即CMB阶段IV实验可以改善$γ_\ text {nfs}（z）/h（z）/h（z）$的界限，最高为$ 10 $。此外，我们对大规模结构观察的评论，发现正在进行的DESI调查有可能探测相互作用中微子参数空间的未知区域。最后，我们指出了迄今尚未考虑的一个奇特场景，由于某些退化与$ n_s $，$ a_s $和$ h_0 $，普朗克数据仍然允许重组周围的相对较大的互动。可以用CMB-S4对此方案进行全面测试。
Neutrinos are expected to freestream (i.e. not interact with anything) since they decouple in the early Universe at a temperature $T\sim 2~{\rm MeV}$. However, there are many relevant particle physics scenarios that can make neutrinos interact at $T< 2~{\rm MeV}$. In this work, we take a global perspective and aim to identify the temperature range in which neutrinos can interact given current cosmological observations. We consider a generic set of rates parametrizing neutrino interactions and by performing a full Planck cosmic microwave background (CMB) analysis we find that neutrinos cannot interact significantly for redshifts $2000 \lesssim z \lesssim 10^5$, which we refer to as the freestreaming window. We also derive a redshift dependent upper bound on a suitably defined interaction rate $Γ_\text{nfs}(z)$, finding $Γ_\text{nfs}(z)/H(z)\lesssim 1-10$ within the freestreaming window. We show that these results are largely model independent under some broad assumptions, and contextualize them in terms of neutrino decays, neutrino self-interactions, neutrino annihilations, and majoron models. We provide examples of how to use our model independent approach to obtain bounds in specific scenarios, and demonstrate agreement with existing results. We also investigate the reach of upcoming cosmological data finding that CMB Stage-IV experiments can improve the bound on $Γ_\text{nfs}(z)/H(z)$ by up to a factor $10$. Moreover, we comment on large-scale structure observations, finding that the ongoing DESI survey has the potential to probe uncharted regions of parameter space of interacting neutrinos. Finally, we point out a peculiar scenario that has so far not been considered, and for which relatively large interactions around recombination are still allowed by Planck data due to some degeneracy with $n_s$, $A_s$ and $H_0$. This scenario can be fully tested with CMB-S4.
