Informal Pizza Seminar

Illuminate the dark energy and see the backreaction!
Take the universe as it is: structured FRW

Reza Mansouri

McGill

We propose a model universe in the matter dominated phase described by a FRW background with local inhomogeneities, like our local patch. Our local patch is approximated as an inhomogeneous cosmic fluid described by a LTB metric embedded in a background FRW universe. The junction conditions for the only possible matching without a thin shell at the boundary constrains the model in such a way that the luminosity distance-red shift relation mimics a FRW universe with dark energy. The existence of the overdense and the compensating underdense regions within the epoch of transition at about z=0.5, a consequence of the junction conditions, explains naturally the late ISW effect and the suppression of low l multipoles in CMB data. The backreaction in the average Einstein equations turns out to have an interesting behavior. Its equivalent density and pressure, being proportional, are negative at early times of the dark ages of the universe, and change sign near our present time in our local patch. In addition to explaining the observed dimming of the SNIa it leads to new effects for small cosmic redshifts and also to the difference between the local and global Hubble parameter. Interpreting the backreaction in the FRW-picture, it is equivalent to a time dependent dark energy with w=-1.

References:
astro-ph/0512605,
astro-ph/0601699.