Comparing early dark energy and extra radiation solutions to the Hubble tension with BBN

TL;DR

This paper compares early dark energy and extra radiation models as solutions to the Hubble tension, analyzing their fit to BBN data and their impact on the inferred Hubble constant, finding the co-existing model yields the highest H0.

Contribution

It provides a comparative analysis of EDE, extra radiation, and combined models, focusing on their consistency with BBN and implications for the Hubble tension.

Findings

EDE models fit BBN less well than ΛCDM due to baryon asymmetry effects.

The combined EDE and extra radiation model predicts the highest Hubble constant.

The effective number of neutrino species N_eff varies significantly depending on BBN data inclusion.

Abstract

The shorten sound horizon scale at the recombination epoch by introducing extra energy components such as the extra radiation or early dark energy (EDE) is a simple approach to so-called the Hubble tension. We compare EDE models, an extra radiation model and an EDE and extra radiation co-existing model with paying attention to the fit to big bang nucleosynthesis (BBN). We find that a fit to BBN in EDE models also is somewhat poorer than that in the $\Lambda$CDM model, because the increased inferred baryon asymmetry leads to smaller deuterium abundance. We find that an extra radiation-EDE co-existing model indicates the largest present Hubble parameter $H_0$ between models studied. We also the examine data sets dependence, whether we include BBN or not. The difference in an extra radiation model is $3.22 < N_\mathrm{eff} < 3.49 \,(68 \%)$ for data sets without BBN and $3.16 < N_\mathrm{eff} < 3.40 \,(68 \%)$ for data sets with BBN, and is so large that the $1\sigma$ border of the larger side becomes the $2\sigma$ border.