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Paper   IPM / Astronomy / 12435
School of Astronomy
  Title:   Modified Averaging Process in Cosmology and the structured FRW Model
1.  Sh. Khosravi
2.  E. Kourkchi
3.  R. Mansouri
  Status:   Published
  Journal: IJMPC
  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 back-reaction fluid. It is shown that, contrary to the claims in the literature, the back-reaction 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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