Double the axions, half the tension: multi-field early dark energy eases the Hubble tension

TL;DR

Multi-field early dark energy models, especially with two fields, can reduce the tension between Planck CMB data and local measurements of the Hubble constant, offering a potential solution to the Hubble tension.

Contribution

The paper demonstrates that multi-field axion-like early dark energy models alleviate Planck constraints and improve fit to high-$ell$ CMB data, with two fields being optimal.

Findings

2-field model reduces Hubble tension to 1.5 sigma

Adding more than two fields does not improve the fit further

Second field enhances fit to high-$ell$ CMB data and modifies pre-recombination history

Abstract

We show that the strong constraints placed by Planck NPIPE Cosmic Microwave Background (CMB) data on axion-like early dark energy (EDE) are significantly alleviated in models with multiple fields. We find a $1.5\sigma$ residual tension with the Local Distance Network value of $H_0$ in a 2-field model, with no improvement beyond two fields, and a best-fit value of $H_0$ $\sim 1.4\sigma$ larger than in the 1-field case. The second field improves the fit to high-$\ell$ CMB data, where 1-field EDE is most strongly disfavored, and suggests modifications to the pre-recombination history over a wider redshift range.