Alleviating both H0 and S8 tensions: Early dark energy lifts the CMB-lockdown on ultralight axion

Abstract

The existence of ultralight axion (ULA) with mass O(10−26eV) is not favored by the CMB observations in the standard ΛCDM model. We show that the inclusion of early dark energy (EDE) will lift the CMB-lockdown on such ULA, and possibly other forms of dark matter beyond cold dark matter. By performing Monte Carlo Markov Chain analysis, it is found that, as opposed to ΛCDM, the AdS-EDE cosmology (with an Anti-de Sitter phase around recombination) now allows the existence of axion with mass 10−26 eV and predicts 6% of the matter in our Universe to be such ULA, which can also help alleviating the S8 tension in EDE.