创建统计各向异性和非均匀扰动
Creating Statistically Anisotropic and Inhomogeneous Perturbations
摘要：
在几乎所有的结构形成模型中，原始扰动都是在均匀和各向同性的宇宙中产生的，就像我们观察到的那样。因为它们的系综平均继承了它们所处时空的对称性，所以宇宙学扰动恰好是统计上各向同性和均匀的。另一方面，宇宙微波背景中的某些异常现象表明，微扰并不满足这些统计特性，从而可能挑战我们对结构形成的理解。在这篇文章中，我们放松这种紧张。我们表明，如果宇宙中包含一个适当的三元组的标量场的空间常数，但非零梯度，它是可能产生统计各向异性和非均匀的原始扰动，即使能量动量张量的三元组本身是不变的平移和旋转。
英文摘要：
In almost all structure formation models, primordial perturbations are created within a homogeneous and isotropic universe, like the one we observe. Because their ensemble averages inherit the symmetries of the spacetime in which they are seeded, cosmological perturbations then happen to be statistically isotropic and homogeneous. Certain anomalies in the cosmic microwave background on the other hand suggest that perturbations do not satisfy these statistical properties, thereby challenging perhaps our understanding of structure formation. In this article we relax this tension. We show that if the universe contains an appropriate triad of scalar fields with spatially constant but non-zero gradients, it is possible to generate statistically anisotropic and inhomogeneous primordial perturbations, even though the energy momentum tensor of the triad itself is invariant under translations and rotations.
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