Resolving the Hubble tension with new early dark energy

Abstract

New early dark energy (NEDE) is a component of vacuum energy at the electron volt scale, which decays in a first-order phase transition shortly before recombination [F. Niedermann and M. S. Sloth, New early dark energy]. The NEDE component has the potential to resolve the tension between recent local measurements of the expansion rate of the Universe using supernovae (SN) data and the expansion rate inferred from the early Universe through measurements of the cosmic microwave background (CMB) when assuming ΛCDM. We discuss in depth the two-scalar field model of the NEDE phase transition including the process of bubble percolation, collision, and coalescence. We also estimate the gravitational wave signal produced during the collision phase and argue that it can be searched for using pulsar timing arrays. In a second step, we construct an effective cosmological model, which describes the phase transition as an instantaneous process, and derive the covariant equations that match perturbations across the transition surface. Fitting the cosmological model to CMB, baryonic acoustic oscillations, and SN data, we report H 0 ¼ 69.6 þ1.0 −1.3 km s −1 Mpc −1 (68% C.L.) without the local measurement of the Hubble parameter, bringing the tension down to 2.5σ. Including the local input, we find H 0 ¼ 71.4 AE 1.0 km s −1 Mpc −1 (68% C.L.) and strong evidence for a nonvanishing NEDE component with a ≃4σ significance.

Constraining early dark energy with large-scale structure

“…We note that our conclusions are different from the recent results of Ref. [46]. However, the analysis in Ref, [46] does not use the full-shape BOSS likelihood and implements a nonstandard method in the f EDE → 0 limit, in which some EDE parameters are held fixed rather than varied in the MCMC.…”

“…[46]. However, the analysis in Ref, [46] does not use the full-shape BOSS likelihood and implements a nonstandard method in the f EDE → 0 limit, in which some EDE parameters are held fixed rather than varied in the MCMC. It would be interesting to see if the discrepancy in results prevails once the same pipeline is used.…”

“…The purpose of this experiment is to clarify if the dearth of evidence for EDE in the CMB and LSS datasets is an artifact of the sampler failing to sufficiently explore parameter space, owing to the parameter degeneracies that emerge in the ΛCDM limit f EDE → 0, as claimed in, e.g., Refs. [26] and [46]. If this were true, then one would expect that an MCMC analysis with f EDE strictly bigger than a certain threshold value would lead to qualitatively different TABLE IV.…”

“…Finally, we perform an additional test of our analyses, detailed in Appendix C. It has been suggested [26,46] that the null results of searches for EDE in combined datasets that do not include the SH0ES measurement are due to a failure of the Metropolis-Hastings algorithm to explore the EDE parameter space, stemming from parameter degeneracies that emerge in the ΛCDM limit, f EDE → 0. This would suggest the existence of an as-yet hidden region of EDE parameter space that is able to accommodate both the local and cosmological datasets, despite being strongly excluded by the MCMC analyses heretofore performed.…”

“…Even though this method is referred to in the literature as the full-shape BOSS analysis, we stress that no power spectrum shape information is used in this procedure. Therefore, one may wonder to what extent the use of such a ΛCDM-based and fixed-shape likelihood may have impacted the conclusions of previous analyses for the EDE model [25][26][27]40,46]. Addressing this question is one of the main goals of this paper.…”