Reconciling $H_0$ tension in a six parameter space?

Abstract

Consistent observations indicate that some of the important cosmological parameters measured through the local observations are in huge tension with their measurements from the global observations (within the minimal $\Lambda$CDM cosmology). The tensions in those cosmological parameters have been found to be either weakened or reconciled with the introduction of new degrees of freedom that effectively increases the underlying parameter space compared to the minimal $\Lambda$CDM cosmology. It might be interesting to investigate the above tensions within the context of an emergent dark energy scenario proposed recently by Li and Shafieloo~\cite{Li:2019yem}. We find that the tension on $H_0$ is clearly alleviated within 68\% confidence level with an improvement of the $\chi^2$ for CMB, for the above emergent dark energy model having only six free parameters similar to the spatially flat $\Lambda$CDM model. The tension on $H_0$ is still alleviated for every combined datasets considered in the work, however, such alleviation occurs by worsening the $\chi^2$ compared to the $\chi^2$ for $\Lambda$CDM model obtained for the same combined dataset.