Baryons do trace dark matter 380,000 years after the big bang: Search for compensated isocurvature perturbations with WMAP 9-year data
Baryons do trace dark matter 380,000 years after the big bang: Search for compensated isocurvature perturbations with WMAP 9-year data
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重子确实在大爆炸后 380,000 年追踪暗物质：利用 WMAP 9 年数据搜索补偿等曲率扰动
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发表时间：
2013
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影响因子：
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通讯作者：
M. Kamionkowski
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作者：
D. Grin;D. Hanson;G. Holder;O. Dor'e;M. Kamionkowski
光子与中微子或重子或暗物质等非相对论性物质之间的原始等曲率涨落被认为是绝热涨落的次优势。然而，重子和暗物质相对密度的扰动（称为补偿等曲率扰动或CIP）令人惊讶地受到很差的约束。在可观测尺度上，CIP在宇宙微波背景（CMB）中没有留下任何印记，至少在其振幅的线性级和绝热扰动振幅的零级。因此，重子是否在最后一次散射的表面追踪到暗物质，还没有经验上的了解。如果CIP存在，它们将在空间上调制丝绸阻尼尺度和声学视界，导致整个天空中CMB温度/偏振功率谱的明显波动：这种效应在CIP和绝热模式振幅中都是一阶的。在这里，温度数据从威尔金森微波各向异性探测器（WMAP）进行的第一个基于CMB的观测搜索CIP，使用非对角相关和CMB三谱。弱透镜和点源的重建噪声被证明是可以忽略不计的这个数据集。没有观察到CIP的证据，并且对标度不变CIP功率谱的幅度施加了1.1×10^（−2）的95%置信上限。这一限制同意CIP的灵敏度预测WMAP和竞争力的小尺度的限制，从测量星系团中的重子分数。结果表明，在95%置信水平下，5-100°尺度上的CIP振幅的均方根小于0.07-0.17（取决于尺度）。来自普朗克卫星的温度数据将为CIP的存在提供更灵敏的探测器，即将进行的ACTPol和SPTPol实验也将在更小的角度范围内进行。
Primordial isocurvature fluctuations between photons and either neutrinos or nonrelativistic species such as baryons or dark matter are known to be subdominant to adiabatic fluctuations. Perturbations in the relative densities of baryons and dark matter (known as compensated isocurvature perturbations or CIPs), however, are surprisingly poorly constrained. CIPs leave no imprint in the cosmic microwave background (CMB) on observable scales, at least at linear order in their amplitude and zeroth order in the amplitude of adiabatic perturbations. It is thus not yet empirically known if baryons trace dark matter at the surface of last scattering. If CIPs exist, they would spatially modulate the Silk damping scale and acoustic horizon, causing distinct fluctuations in the CMB temperature/polarization power spectra across the sky: this effect is first order in both the CIP and adiabatic mode amplitudes. Here, temperature data from the Wilkinson Microwave Anisotropy Probe (WMAP) are used to conduct the first CMB-based observational search for CIPs, using off-diagonal correlations and the CMB trispectrum. Reconstruction noise from weak lensing and point sources is shown to be negligible for this data set. No evidence for CIPs is observed, and a 95% confidence upper limit of 1.1×10^(−2) is imposed to the amplitude of a scale-invariant CIP power spectrum. This limit agrees with CIP sensitivity forecasts for WMAP and is competitive with smaller-scale constraints from measurements of the baryon fraction in galaxy clusters. It is shown that the root-mean-squared CIP amplitude on 5–100° scales is smaller than ∼0.07–0.17 (depending on the scale) at the 95% confidence level. Temperature data from the Planck satellite will provide an even more sensitive probe for the existence of CIPs, as will the upcoming ACTPol and SPTPol experiments on smaller angular scales.