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

TL;DR

This paper explores how early dark energy and deviations in neutrino properties could resolve discrepancies in primordial helium measurements and the Hubble constant tension.

Contribution

It investigates the impact of early dark energy and non-standard neutrino properties on cosmological models in light of recent helium abundance measurements.

Findings

Early dark energy can alleviate tensions from EMPRESS $Y_p$ results.

Deviations in neutrino number and lepton asymmetry impact primordial element abundances.

Higher baryon density may help resolve the Hubble 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.