Big bang nucleosynthesis and early dark energy in light of the EMPRESS $Y_p$ results and the $H_0$ tension

Abstract

Recent measurement of the primordial $^4$He abundance $Y_p$ from EMPRESS suggests a cosmological scenario with the effective number of neutrino species deviated from the standard value and non-zero lepton asymmetry. We argue that the extension of the standard cosmological model would be more demanded when the Hubble tension is taken into account, in which derived baryon density could be somewhat higher than the standard $\Lambda$CDM framework. We also discuss the issue by assuming early dark energy whose energy density can have a sizable fraction at the epoch of big bang nucleosynthesis. We show that the existence of early dark energy can reduce some tension implied by the EMPRESS $Y_p$ results.