Structure Formation, Backreaction and Weak Gravitational Fields

Understand

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.