暗能量指纹III：粘性的独特标记
Fingerprinting Dark Energy III: distinctive marks of viscosity
摘要：
表征暗能量是宇宙学的主要目标之一，特别是现在许多新的实验正在计划中，目的是达到对宇宙学参数的高灵敏度。众所周知，如果我们离开简单的宇宙学常数模型，那么我们需要考虑暗能量流体中的扰动。这意味着暗能量有两个额外的自由度：声速$\cs$和各向异性应力$σ$。如果暗能量在感兴趣的尺度上是不均匀的，那么引力势就会被修改，暗物质扰动的演化也会直接受到影响。本文在暗能量扰动中加入了各向异性分量。在\cite{Sapone:2009mb}中引入的思想之后，我们解析地求解了暗扇区中的扰动方程，找到了简单而精确的近似解。我们还发现，密度扰动的演变是由一个有效的声速取决于声速和各向异性应力参数。然后，我们使用这些解决方案，看看在暗能量扰动的影响，对物质的功率谱和综合萨克斯-沃尔夫效应的宇宙微波背景。
英文摘要：
The characterisation of dark energy is one of the primary goals in cosmology especially now that many new experiments are being planned with the aim of reaching a high sensitivity on cosmological parameters. It is known that if we move away from the simple cosmological constant model then we need to consider perturbations in the dark energy fluid. This means that dark energy has two extra degrees of freedom: the sound speed $\cs$ and the anisotropic stress $σ$. If dark energy is inhomogenous at the scales of interest then the gravitational potentials are modified and the evolution of the dark matter perturbations is also directly affected. In this paper we add an anisotropic component to the dark energy perturbations. Following the idea introduced in \cite{Sapone:2009mb}, we solve analytically the equations of perturbations in the dark sector, finding simple and accurate approximated solutions. We also find that the evolution of the density perturbations is governed by an effective sound speed which depends on both the sound speed and the anisotropic stress parameter. We then use these solutions to look at the impact of the dark energy perturbations on the matter power spectrum and on the Integrated Sachs-Wolfe effect in the Cosmic Microwave Background.
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