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arXiv 1306.1536astro-ph.COhep-ph
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早期宇宙中中微子-中微子散射的极限

Limits on Neutrino-Neutrino Scattering in the Early Universe

Francis-Yan Cyr-Racine, Kris Sigurdson

备注：
9 Pages, 4 figures, 1 table. v2: Version accepted for publication, enhanced discussion on neutrino interaction beyond the SM, enhanced figures, references added
发表信息：
Phys. Rev. D 90, 123533 (2014)
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摘要：

在标准模型中，中微子被假定为在宇宙中流动，因为它们最后一次散射是在弱退耦时期，当时标准模型等离子体的温度为~MeV。自由流中微子的剪切应力在宇宙微波背景（CMB）上留下引力印记，使CMB成为中微子散射的灵敏探针。然而，中微子领域中非标准物理的存在可能会改变这一标准年表，并将中微子自由流推迟到更晚的时代。我们利用CMB的观测结果来限制中微子自相互作用G_eff的强度，并限制早期宇宙中微子领域的新物理。最近的测量CMB在大多极普朗克卫星和高-l实验是至关重要的探测这一物理。在常规λ CDM参数的背景下，宇宙学数据与G_eff <1/（56 MeV）^[2]是一致的，中微子自由流可能会延迟到它们的温度冷却到约25 eV。有趣的是，我们还发现了另一种与宇宙学数据相一致的宇宙学，即中微子在$G_{\rm eff} \simeq 1/({\rm 10 \, MeV})^{2} \simeq 8.6\times10^8 G_{\rm F}$附近的一个狭窄区域内相互散射，直到z~10 ^4，并且具有优选的相互作用强度，其中$G_{\rm F}$是费米常数。这种独特的自相互作用中微子宇宙学的特点是标量光谱指数和原始波动的幅度都略低。虽然我们在这里的讨论是根据一个特定的场景，在这个场景中，中微子自由流可能会发生延迟，但我们对中微子可见度函数的限制是非常普遍的。

英文摘要：

In the standard model neutrinos are assumed to have streamed across the Universe since they last scattered at the weak decoupling epoch when the temperature of the standard-model plasma was ~MeV. The shear stress of free-streaming neutrinos imprints itself gravitationally on the Cosmic Microwave Background (CMB) and makes the CMB a sensitive probe of neutrino scattering. Yet, the presence of nonstandard physics in the neutrino sector may alter this standard chronology and delay neutrino free-streaming until a much later epoch. We use observations of the CMB to constrain the strength of neutrino self-interactions G_eff and put limits on new physics in the neutrino sector from the early Universe. Recent measurements of the CMB at large multipoles made by the Planck satellite and high-l experiments are critical for probing this physics. Within the context of conventional LambdaCDM parameters cosmological data are compatible with G_eff < 1/(56 MeV)^2 and neutrino free-streaming might be delayed until their temperature has cooled to as low as ~25 eV. Intriguingly, we also find an alternative cosmology compatible with cosmological data in which neutrinos scatter off each other until z~10^4 with a preferred interaction strength in a narrow region around $G_{\rm eff} \simeq 1/({\rm 10 \, MeV})^{2} \simeq 8.6\times10^8 G_{\rm F}$, where $G_{\rm F}$ is the Fermi constant. This distinct self-interacting neutrino cosmology is characterized by somewhat lower values of both the scalar spectral index and the amplitude of primordial fluctuations. While we phrase our discussion here in terms of a specific scenario in which a late onset of neutrino free-streaming could occur, our constraints on the neutrino visibility function are very general.

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