The Hubble expansion rate inferred from the Planck CMB data is H0 = 67.36 ± 0.54 km/s/Mpc, which is 5 sigma discrepant with the latest measurement of H0 from supernovae IA calibrated using Cepheids H0 = 73.04 ± 1.04 km/s/Mpc. This tension motivates a revisit of the data analysis on both sides to assess the robustness of cosmological parameter determination. We present a re-analysis of Planck CMB data using the correlation coefficient of T and E modes, a new observable robust against multiplicative instrumental systematic effects. A second way of resolving the tension is to introduce new physics in the early Universe in order to reconcile early and late time measurements of H0. We will discuss one of the proposed solutions : Early Dark Energy (EDE), in which a new field is introduced to accelerate expansion before recombination. We will discuss the latest constraints on this model from the Planck satellite and from ground-based experiments such as the Atacama Cosmology Telescope and the South Pole Telescope.
