Big bang nucleosynthesis and early dark energy in light of the EMPRESS Yp results and the H0 tension

Abstract

Recent measurements of the primordial $^{4}\mathrm{He}$ abundance ${Y}_{p}$ from EMPRESS suggest a cosmological scenario with an effective number of neutrino species that deviates from the standard value and a nonzero lepton asymmetry. We argue that the standard cosmological model would be extended further if the Hubble tension were taken into account, in which the derived baryon density could be somewhat higher than the in the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ 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 of the tension implied by the EMPRESS ${Y}_{p}$ results.