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Paper   IPM / Physic / 8688
School of Physics
  Title:   Modified averaging processes in cosmology and the structured FRW model
1.  S. Khosravi
2.  E. Kourkchi
3.  R. Mansouri
  Status:   Published
  Journal: Int. J. Mod. Phys. D
  No.:  7
  Vol.:  18
  Year:  2009
  Pages:   1177-1192
  Supported by:  IPM
We study the volume averaging of inhomogeneous metrics within GR and discuss its shortcomings such as gauge dependence, singular behavior as a result of caustics, and causality violations. To remedy these shortcomings, we suggest some modifications to this method. As a case study we focus on the inhomogeneous structured FRW model based on a flat LTB metric. The effect of averaging is then studied in terms of an effective backreaction fluid. It is shown that, contrary to the claims in the literature, the backreaction fluid behaves like a dark matter component, instead of dark energy, having a density of the order of 10^-5 times the matter density, and most importantly, it is gauge dependent.

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