Early Dark Energy can Resolve the Hubble Tension

Early dark energy (EDE) that behaves like a cosmological constant at early times (redshifts $z\gtrsim 3000$) and then dilutes away like radiation or faster at later times can solve the Hubble tension. In these models, the sound horizon at decoupling is reduced resulting in a larger value of the Hubble parameter $H_0$ inferred from the cosmic microwave background (CMB). We consider two physical models for this EDE, one involving an oscillating scalar field and another a slowly rolling field. We perform a detailed calculation of the evolution of perturbations in these models. A Markov Chain Monte Carlo search of the parameter space for the EDE parameters, in conjunction with the standard cosmological parameters, identifies regions in which $H_0$ inferred from Planck CMB data agrees with the SH0ES local measurement. In these cosmologies, current baryon acoustic oscillation and supernova data are described as successfully as in the cold dark matter model with a cosmological constant, while the fit to Planck data is slightly improved. Future CMB and large-scale-structure surveys will further probe this scenario.

Figure 1

Comparison between the marginalized 1D and 2D posterior distributions of $H_0$, ${\omega }_{\mathrm{cdm}}$, $f_{\mathrm{EDE}}(a_c)$ and ${\log }_{10}(a_c)$ in the EDE cosmology with $n=2$, $n=3$ and $n=\infty$. The best fit value of $H_0$ in $\mathrm{\Lambda }\mathrm{CDM}$ is shown in orange; the one from SH0ES is shown in grey.

Figure 2

The variation of the scales that are “fixed” by the CMB data with respect to $f_{\mathrm{EDE}}(a_c)$ as a function of $a_c$ with all other cosmological parameters fixed at their Planck best-fit values [6]. The colored bands indicate the marginalized $1\sigma$ range of $a_c$ for each EDE model considered here.

Figure 3

Residuals of the CMB TT (top panel) and EE (bottom panel) power spectra calculated in the best-fit EDE model with respect to $\mathrm{\Lambda }\mathrm{CDM}$, obtained from our MCMC analyses. Blue points show residuals of Planck data, while orange bands show the binned Cosmic Variance with the same bins and weights as Planck.