结构形成、反作用与弱引力场
Structure Formation, Backreaction and Weak Gravitational Fields
摘要：
在文献中有一个持续的争论，关于宇宙学中平均不均匀性（“反作用”）的影响是否足够大，以解释FLRW模型中尺度因子的加速。特别是，在文献中研究的结构形成的一些简单的模型似乎表明，这确实是可能的，它也被认为是扰动FLRW框架不再是一个很好的近似在结构形成过程中，当密度对比变得非线性。在这项工作中，我们试图澄清的情况在一定程度上，使用完全相对论模型的无压球形崩溃。我们发现，而平均结构形成过程中可以通过选择性选择的平均域加速，加速不存在时，更通用的域用于平均。此外，我们表明，对于大部分的崩溃的持续时间，物质的速度仍然很小，扰动FLRW形式的度量可以明确地恢复，在结构形成阶段。我们还讨论了这样一个事实，即不均匀性的平均影响的大小取决于平均的规模，虽然它可能不会完全忽略不计的中间规模，预计将保持在适当的大规模平均时小。
英文摘要：
There is an ongoing debate in the literature as to whether the effects of averaging out inhomogeneities (``backreaction'') in Cosmology can be large enough to account for the acceleration of the scale factor in the FLRW models. In particular, some simple models of structure formation studied in the literature seem to indicate that this is indeed possible, and it has also been suggested that the perturbed FLRW framework is no longer a good approximation during structure formation, when the density contrast becomes nonlinear. In this work we attempt to clarify the situation to some extent, using a fully relativistic model of pressureless spherical collapse. We find that whereas averaging during structure formation can lead to acceleration via a selective choice of averaging domains, the acceleration is not present when more generic domains are used for averaging. Further, we show that for most of the duration of the collapse, matter velocities remain small, and the perturbed FLRW form of the metric can be explicitly recovered, in the structure formation phase. We also discuss the fact that the magnitude of the average effects of inhomogeneities depends on the scale of averaging, and while it may not be completely negligible on intermediate scales, it is expected to remain small when averaging on suitably large scales.
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