Observational tests of backreaction with recent data

TL;DR

This paper tests the backreaction cosmological model using recent supernova, cluster, and CMB data, finding inconsistencies in matter density predictions at recombination.

Contribution

It provides observational constraints on the backreaction model parameters using multiple datasets and highlights an inconsistency in matter density predictions at recombination.

Findings

Backreaction model suggests higher matter density than Friedmann models.

Cluster and supernova data support higher matter density in backreaction models.

CMB data indicates a lower matter density at recombination, conflicting with other observations.

Abstract

We explore the backreaction model based on the template metric proposed in Larena et al. (2008) constraining the matter density parameter $\Omega_m^{D_0}$ and the Dark Energy parameter $w$ with recent data. We provide constraints based on Supernovae Ia from the SNLS and the Union2.1 catalogs, confirming that the backreacted Universe should have a higher matter density than the corresponding Friedmaniann one. Angular diameter distances from clusters data confirm the same feature. Finally we combine these results with constraints obtained from the position of the first three peaks and the first dip of the CMB power spectrum, fitting WMAP-9 and Planck data. We find that an inconsistency arises in predicting the scale factor at recombination, leading to a backreacted Universe with lower matter density, in contradiction with results produced by SnIa and clusters. The same behavior is confirmed by analyzing the CMB-shift parameters from WMAP-9. We conclude exploring qualitatively the motivations of this inconsistency.