The Hubble tension describes the discrepancy between two measurements of the expansion rate of the Universe. One measurement relies on supernovae as standard candles in a low-redshift patch around our position in space and the other one infers the value of the Hubble constant from measurements of the cosmic microwave background. After briefly reviewing the tension, I will argue that it might be the signature of new physics in the early Universe. In particular, it could be related to a new phase of dark energy that decays in a first order phase transition before the Universe becomes transparent during recombination. I will present the physics of two distinct models that rely on this idea, Cold and Hot New Early Dark Energy. Both models come with unique signatures that can be looked for in the CMB, the large-scale-structure of the Universe, and gravitational wave experiments.
Organized by: Catarina Cosme