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arXiv 2207.04062astro-ph.COhep-ph
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宇宙学中中微子相互作用的全局观:普朗克观测到的自由游动窗口

Global view of neutrino interactions in cosmology: The freestreaming window as seen by Planck

Petter Taule, Miguel Escudero, Mathias Garny

摘要:

中微子被认为是自由跃迁的(即不与任何东西相互作用),因为它们在早期宇宙中的温度为$T\sim 2~{\rm MeV}$。然而,有许多相关的粒子物理场景可以使中微子在$T< 2~{\rm MeV}$发生相互作用。在这项工作中,我们采取了全球性的观点,并旨在确定中微子可以相互作用的温度范围,给出当前的宇宙学观测。我们考虑一组通用的速率参数化中微子的相互作用,并通过执行一个完整的普朗克宇宙微波背景(CMB)分析,我们发现,中微子不能相互作用显着的红移$2000 \lesssim z \lesssim 10^5$,我们称之为freestreaming窗口。我们还推导出一个红移依赖的上限上适当定义的相互作用速率$Γ_\text{nfs}(z)$,发现$Γ_\text{nfs}(z)/H(z)\lesssim 1-10$内的freestreaming窗口。我们发现,这些结果在很大程度上是模型独立的一些广泛的假设下,和上下文的中微子衰变,中微子自相互作用,中微子湮灭,和majoron模型。我们提供的例子,如何使用我们的模型独立的方法来获得在特定情况下的界限,并证明与现有结果的协议。我们还调查了即将到来的宇宙学数据的范围,发现CMB第四阶段的实验可以提高$Γ_\text{nfs}(z)/H(z)$的约束高达一个因子$10$。此外,我们评论大规模的结构观测,发现正在进行的DESI调查有可能探测未知区域的相互作用中微子的参数空间。最后,我们指出了一个奇特的情况下,到目前为止还没有被考虑到,相对较大的相互作用周围的重组仍然允许普朗克数据由于一些简并与$n_s$,$A_s$和$H_0$。这个场景可以用CMB-S4进行全面测试。

英文摘要:

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.

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