Observable cosmological vector mode in the dark ages
Observable cosmological vector mode in the dark ages
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DOI：
10.1103/physrevd.94.063523
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发表时间：
2016-07
影响因子：
5
通讯作者：
S. Saga
中科院分区：
文献类型：
--
作者：
S. Saga
二阶矢量模式不可避免地是由宇宙学摄动理论中一阶标量模式的耦合引起的，并且可能阻碍通过 21cm 透镜观测探测暴胀产生的原初引力波。在这里，我们通过将21cm透镜信号的偏转角分解为梯度模式和旋度模式，研究了黑暗时代中性氢原子发射的21cm光子中二阶矢量模式引起的弱透镜信号。旋度模式是宇宙学矢量和张量模式的良好示踪剂，因为标量模式不会引发旋度模式。通过比较二阶矢量模式引起的21cm透镜卷曲模式和振幅由张量与标量比$r$参数化的原初引力波的角功率谱，我们发现，如果$r \lesssim 10^{-5}$，二阶矢量模式的21cm卷曲模式在几乎所有尺度上都优于原初引力波。如果我们使用高达 $\ell_{\rm max} = 10^{5}$ 和 $10^{6}$ 的功率谱多极子来从 21cm 温度图重建卷曲模式，则二阶矢量模式的 21cm 卷曲模式的信噪比分别达到 ${\rm S/N} \approx 0.46$ 和 $73$。原则上，21cm辐射的观测不仅是探索张量模式而且是探索宇宙矢量模式的有力工具。
The second-order vector mode is inevitably induced from the coupling of first-order scalar modes in cosmological perturbation theory and might hinder a possible detection of primordial gravitational waves from inflation through 21cm lensing observations. Here, we investigate the weak lensing signal in 21cm photons emitted by neutral hydrogen atoms in the dark ages induced by the second-order vector mode by decomposing the deflection angle of the 21cm lensing signal into the gradient and curl modes. The curl mode is a good tracer of the cosmological vector and tensor modes since the scalar mode does not induce the curl one. By comparing angular power spectra of the 21cm lensing curl mode induced by the second-order vector mode and primordial gravitational waves whose amplitude is parametrized by the tensor-to-scalar ratio $r$, we find that the 21cm curl mode from the second-order vector mode dominates over that from primordial gravitational waves on almost all scales if $r \lesssim 10^{-5}$. If we use the multipoles of the power spectrum up to $\ell_{\rm max} = 10^{5}$ and $10^{6}$ in reconstructing the curl mode from 21cm temperature maps, the signal-to-noise ratios of the 21cm curl mode from the second-order vector mode achieve ${\rm S/N} \approx 0.46$ and $73$, respectively. Observation of 21cm radiation is, in principle, a powerful tool to explore not only the tensor mode but also the cosmological vector mode.