The expansion rate of the intermediate Universe in light of Planck

TL;DR

This study compares cosmology-independent expansion history measurements with Planck predictions to investigate the Hubble tension across redshifts, finding no tension within 0.1<z<1.2 but a significant overall discrepancy.

Contribution

It provides the first comprehensive comparison of expansion history data with Planck predictions across a broad redshift range, clarifying the Hubble tension's redshift dependence.

Findings

No tension between Planck and independent measurements at 0.1<z<1.2.

Significant tension when combining all data sets, confirming the Hubble constant discrepancy.

Constraints on H0 and Omega_m without CMB priors.

Abstract

We use cosmology-independent measurements of the expansion history in the redshift range 0.1 < z <1.2 and compare them with the Cosmic Microwave Background-derived expansion history predictions. The motivation is to investigate if the tension between the local (cosmology independent) Hubble constant H0 value and the Planck-derived H0 is also present at other redshifts. We conclude that there is no tension between Planck and cosmology independent-measurements of the Hubble parameter H(z) at 0.1 < z < 1.2 for the LCDM model (odds of tension are only 1:15, statistically not significant). Considering extensions of the LCDM model does not improve these odds (actually makes them worse), thus favouring the simpler model over its extensions. On the other hand the H(z) data are also not in tension with the local H0 measurements but the combination of all three data-sets shows a highly significant tension (odds ~ 1:400). Thus the new data deepen the mystery of the mismatch between Planck and local H0 measurements, and cannot univocally determine wether it is an effect localised at a particular redshift. Having said this, we find that assuming the NGC4258 maser distance as the correct anchor for H0, brings the odds to comfortable values. Further, using only the expansion history measurements we constrain, within the LCDM model, H0 = 68.5 +- 3.5 and Omega_m = 0.32 +- 0.05 without relying on any CMB prior. We also address the question of how smooth the expansion history of the universe is given the cosmology independent data and conclude that there is no evidence for deviations from smoothness on the expansion history, neither variations with time in the value of the equation of state of dark energy.