1805.09000
The impact of the cosmic variance on $H_0$ on cosmological analyses
Camarena, Marra
The current 3.4 sigma tension between local (1604.01424) and global (1605.02985) measurements of H_0 cannot be fully explained by the concordance LCDM model. It could be produced by unknown systematics or by physics beyond the standard model. In particular, non-standard DE models were shown to be able to alleviate this tension. On the other hand, it is well known that linear perturbation theory predicts a cosmic variance on the Hubble parameter H_0, which leads to systematic errors on its local determination. Here, study how including in the likelihood the cosmic variance on H_0 affects statistical inference. In particular, consider the gammaCDM, wCDM and gamma w CDM parametric extensions of the standard model, which is constrained with CMB, BAO, NSeIa, RSD and H_0 data. Learn two important lessons. First, the systematic error from cosmic variance is -- independently of the model - approximately sigma_cv ~ 2 km/s/Mpc and of the same order of the uncertainty 1.74 km/s/Mpc on local H_0. Taking into account cosmic variance, the tension is reduced to 2.4 sigma so that the cosmology-independent estimate by Riess+ (1604.01424) can be included in cosmological analyses without the risk of artificially biasing the results. Second, cosmic variance, besides shifting the constraints, can drastically change the results of model selection: much of the statistical advantage of non-standard models is to alleviate the now-reduced tension. Conclude that it is crucial to include the cosmic variance on H_0 if one wants to use the local determination of the Hubble constant by Riess+. Doing the contrary could potentially bias the conclusions.
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