Constraining primordial vector mode from B-mode polarization
Constraining primordial vector mode from B-mode polarization
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DOI：
10.1088/1475-7516/2014/10/004
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发表时间：
2014-05
影响因子：
6.4
通讯作者：
S. Saga;M. Shiraishi;K. Ichiki
中科院分区：
文献类型：
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作者：
S. Saga;M. Shiraishi;K. Ichiki
宇宙微波背景（CMB）的b模偏振谱不仅可能是原始张量模式的确凿证据，也可能是原始矢量模式的确凿证据。如果在早期宇宙中存在非零矢量模度量扰动，那么已知它们是由自由流动的粒子（如中微子）的各向异性应力波动所支持的，并且在CMB温度、e模和b模极化各向异性上都产生了特征特征。我们从普朗克和BICEP2的b模式数据中对原始矢量模式的性质进行了约束，其特征是矢量与标量比rv和矢量剪切功率谱的谱指数nv。我们发现，对于尺度不变的初始谱，包含矢量模态的ΛCDM模型比包含张量模态的模型更能拟合数据。矢量模型和张量模型的χ2差异为Δχ2 = 3.294，因为在大尺度上，矢量模型比张量模型产生的温度波动更小，这对数据更有利。相反，如果我们允许显著的蓝倾斜光谱，张量模式可以同样很好地拟合数据集。我们发现最佳拟合张量模式具有较大的蓝色倾斜，并在较大的角尺度上导致不明显的再电离凸起。当前数据集支持的微红倾斜矢量模式也可以在宇宙学重组中产生<s:1>(10-22)-高斯磁场。我们的限制应该激励研究，考虑早期宇宙的模型，包括矢量模式。
The B-mode polarization spectrum of the Cosmic Microwave Background (CMB) may be the smoking gun of not only the primordial tensor mode but also of the primordial vector mode. If there exist nonzero vector-mode metric perturbations in the early Universe, they are known to be supported by anisotropic stress fluctuations of free-streaming particles such as neutrinos, and to create characteristic signatures on both the CMB temperature, E-mode, and B-mode polarization anisotropies. We place constraints on the properties of the primordial vector mode characterized by the vector-to-scalar ratio rv and the spectral index nv of the vector-shear power spectrum, from the Planck and BICEP2 B-mode data. We find that, for scale-invariant initial spectra, the ΛCDM model including the vector mode fits the data better than the model including the tensor mode. The difference in χ2 between the vector and tensor models is Δχ2 = 3.294, because, on large scales the vector mode generates smaller temperature fluctuations than the tensor mode, which is preferred for the data. In contrast, the tensor mode can fit the data set equally well if we allow a significantly blue-tilted spectrum. We find that the best-fitting tensor mode has a large blue tilt and leads to an indistinct reionization bump on larger angular scales. The slightly red-tilted vector mode supported by the current data set can also create 𝒪(10-22)-Gauss magnetic fields at cosmological recombination. Our constraints should motivate research that considers models of the early Universe that involve the vector mode.