Improved Planck constraints on axion-like early dark energy as a resolution of the Hubble tension

TL;DR

This study uses new Planck CMB data to constrain axion-like early dark energy, finding it cannot fully resolve the Hubble tension and remains consistent with the standard cosmological model.

Contribution

The paper presents a new Planck likelihood analysis that tightens constraints on early dark energy, showing it does not significantly alleviate the Hubble tension.

Findings

EDE fraction constrained to less than 6.1% at 95% CL

Hubble constant range 66.9-69.5 km/s/Mpc at 95% CL

No evidence found supporting a significant EDE component

Abstract

Axion-like early dark energy (EDE) as an extension to $\Lambda$CDM has been proposed as a possible solution to the 'Hubble tension'. We revisit this model using a new cosmic microwave background (CMB) temperature and polarization likelihood constructed from the {\it Planck} NPIPE data release. In a Bayesian analysis, we find that the maximum fractional contribution of EDE to the total energy density is $f_{\rm EDE} < 0.061$ (without SH0ES) over the redshift range $z\in[10^3,10^4]$ and that the Hubble constant is constrained to lie within the range $ 66.9 < H_0 < 69.5$ km/s/Mpc (both at 95 \% C.L.). The data therefore favour a model close to $\Lambda$CDM, leaving a residual tension of $3.7\sigma$ with the SH$0$ES Cepheid-based measurement of $H_0$. A comparison with the likelihood profile shows that our conclusions are robust to prior-volume effects. Our new CMB likelihood provides no evidence in favour of a significant EDE component.