理解Dyer-Roeder近似作为投影剪切和膨胀率波动的局部抵消的结果
Understanding the Dyer-Roeder approximation as a consequence of local cancellations of projected shear and expansion rate fluctuations
摘要：
它示出了几个具体的例子，在时空中的Dyer-Roeder近似是有效的，满足的条件下，沿光线的膨胀率的波动局部抵消剪切贡献的红移。这是标准宇宙学场景的情况，包括扰动FLRW时空，N体模拟和瑞士奶酪模型。用另一个具体的例子说明了不满足条件的统计均匀和有效统计各向同性的宇宙学模型是可能的。在这种情况下，Dyer-Roeder近似是无效的。相反，平均红移-距离关系可以用一个基于时空透明部分的空间平均值的关系来描述。
英文摘要：
It is shown with several concrete examples that the Dyer-Roeder approximation is valid in spacetimes which fulfill the condition that fluctuations in the expansion rate along a light ray locally cancels with the shear contribution to the redshift. This is the case for standard cosmological scenarios including perturbed FLRW spacetimes, N-body simulations and Swiss-cheese models. With another concrete example it is then illustrated that it is possible to construct statistically homogeneous and effectively statistically isotropic cosmological models which do not fulfill the condition. In this case, the Dyer-Roeder approximation is invalid. Instead, the mean redshift-distance relation can be described using a relation based on the spatial averages of the transparent part of the spacetime.
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