Observational evidence for Early Dark Energy as a unified explanation for Cosmic Birefringence and the Hubble tension

Abstract: We test the $n$=3 Ultralight Axion-like model of Early Dark Energy (EDE) with the observationsof the $EB$ mode of the cosmic microwave background (CMB) radiation, and local expansion rate measurements. Our results show that the shape of the CMB $EB$ angular power spectrum is sensitive to the background cosmological parameters. We run Markov chain Monte Carlo (MCMC) simulations to fit the $\Lambda$CDM + EDE parameters simultaneously, and find that the EDE model with $n$=3 can provide a good fit to the observed CMB $EB$ spectra, consistent with the locally measured value of the Hubble constant. Our result is the first to show that axion-like EDE can provide a unified explanation for the observed cosmic birefringence and the Hubble tension.