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New Early Dark Energy

Florian Niedermann, Martin S. Sloth

TL;DR

The paper tackles the Hubble tension by introducing New Early Dark Energy (NEDE), a short-lived epoch driven by a first-order phase transition in a dark sector prior to recombination. It formulates a two-field scalar potential with a tunneling field and a trigger field, derives background and perturbation matching across an instantaneous transition at $t_*$, and implements the model in a Boltzmann code to fit CMB, BAO, and SNe data. The analysis yields a nonzero NEDE fraction, a higher inferred $H_0$ around $71.4$ km s$^{-1}$ Mpc$^{-1}$, and a significant improvement in the fit compared to $\Lambda$CDM, with strong Bayesian evidence when SH0ES data are included. The results suggest NEDE can reconcile early- and late-time measurements without deteriorating other cosmological constraints, and motivate further refinements of the microphysics and perturbation treatment.

Abstract

New measurements of the expansion rate of the Universe have plunged the standard model of cosmology into a severe crisis. In this letter, we propose a simple resolution to the problem that relies on a first order phase transition in a dark sector in the early Universe, before recombination. This will lead to a short phase of a New Early Dark Energy (NEDE) component and can explain the observations. We model the false vacuum decay of the NEDE scalar field as a sudden transition from a cosmological constant source to a decaying fluid with constant equation of state. The corresponding fluid perturbations are covariantly matched to the adiabatic fluctuations of a sub-dominant scalar field that triggers the phase transition. Fitting our model to measurements of the cosmic microwave background (CMB), baryonic acoustic oscillations (BAO, and supernovae (SNe) yields a significant improvement of the best-fit compared with the standard cosmological model without NEDE. We find the mean value of the present Hubble parameter in the NEDE model to be $H_0=71.4 \pm 1.0 ~\textrm{km}\, \textrm{s}^{-1}\, \textrm{Mpc}^{-1}$ ($68\, \%$ C.L.).

New Early Dark Energy

TL;DR

The paper tackles the Hubble tension by introducing New Early Dark Energy (NEDE), a short-lived epoch driven by a first-order phase transition in a dark sector prior to recombination. It formulates a two-field scalar potential with a tunneling field and a trigger field, derives background and perturbation matching across an instantaneous transition at , and implements the model in a Boltzmann code to fit CMB, BAO, and SNe data. The analysis yields a nonzero NEDE fraction, a higher inferred around km s Mpc, and a significant improvement in the fit compared to CDM, with strong Bayesian evidence when SH0ES data are included. The results suggest NEDE can reconcile early- and late-time measurements without deteriorating other cosmological constraints, and motivate further refinements of the microphysics and perturbation treatment.

Abstract

New measurements of the expansion rate of the Universe have plunged the standard model of cosmology into a severe crisis. In this letter, we propose a simple resolution to the problem that relies on a first order phase transition in a dark sector in the early Universe, before recombination. This will lead to a short phase of a New Early Dark Energy (NEDE) component and can explain the observations. We model the false vacuum decay of the NEDE scalar field as a sudden transition from a cosmological constant source to a decaying fluid with constant equation of state. The corresponding fluid perturbations are covariantly matched to the adiabatic fluctuations of a sub-dominant scalar field that triggers the phase transition. Fitting our model to measurements of the cosmic microwave background (CMB), baryonic acoustic oscillations (BAO, and supernovae (SNe) yields a significant improvement of the best-fit compared with the standard cosmological model without NEDE. We find the mean value of the present Hubble parameter in the NEDE model to be ( C.L.).

Paper Structure

This paper contains 7 sections, 14 equations, 2 figures.

Table of Contents

  1. Introduction
  2. The Model
  3. Matching conditions
  4. Background Matching
  5. Perturbation Matching
  6. Data Analysis and Results
  7. Conclusions

Figures (2)

  • Figure 1: Schematic plot of the two-field potential in \ref{['eq:action2']}. For $H ~\hbox{$\stackrel{<}{\sim}$}~ m$, the field rolls along the orange line corresponding to $\psi = 0$. At the inflection point (blue dot) the potential (in $\psi$ direction) develops a second minimum which becomes degenerate shortly after (orange dot). The nucleation probability increases towards $\phi = 0$ (red dot). The true vacuum corresponds to the white dot.
  • Figure 2: Covariances and posteriors of $H_0$, $f_\text{NEDE}$, $z_*$ and $\omega_\text{cdm}$ for our combined analyses. The $68 \%$ and $95 \%$ C.L. correspond respectively to the light and dark shaded regions. The SH$_0$ES value is represented as the vertical gray bands.