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Early Dark Energy Can Resolve The Hubble Tension

Vivian Poulin, Tristan L. Smith, Tanvi Karwal, Marc Kamionkowski

TL;DR

This work considers two physical models for this early dark energy EDE, one involving an oscillating scalar field and another a slowly rolling field, and performs a detailed calculation of the evolution of perturbations in these models.

Abstract

Early dark energy (EDE) that behaves like a cosmological constant at early times (redshifts $z\gtrsim3000$) 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 {\it 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 \LCDM, while the fit to {\it Planck} data is slightly improved. Future CMB and large-scale-structure surveys will further probe this scenario.

Early Dark Energy Can Resolve The Hubble Tension

TL;DR

This work considers two physical models for this early dark energy EDE, one involving an oscillating scalar field and another a slowly rolling field, and performs a detailed calculation of the evolution of perturbations in these models.

Abstract

Early dark energy (EDE) that behaves like a cosmological constant at early times (redshifts ) 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 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 inferred from {\it 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 \LCDM, while the fit to {\it Planck} data is slightly improved. Future CMB and large-scale-structure surveys will further probe this scenario.

Paper Structure

This paper contains 2 equations, 3 figures, 2 tables.

Figures (3)

  • Figure 1: Comparison between the marginalized 1D and 2D posterior distributions of $H_0$, $\omega_{\rm cdm}$, $f_{\rm EDE}(a_c)$ 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 $\Lambda$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 $f_{\rm EDE}(a_c)$ as a function of $a_c$ with all other cosmological parameters fixed at their Planck best-fit values Aghanim:2018eyx. 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 $\Lambda$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.