Profiling Cold New Early Dark Energy

TL;DR

This paper performs a frequentist profile likelihood analysis of the NEDE cosmological model, constraining its parameters and showing it alleviates the Hubble tension more strongly than Bayesian methods.

Contribution

It introduces a frequentist approach to constrain NEDE parameters, providing new insights into prior effects and model comparison with EDE.

Findings

NEDE fraction constrained to about 7.6% without SH0ES prior

Including SH0ES prior increases NEDE fraction to about 13.6%

NEDE model alleviates Hubble tension, with H0 around 69.6 to 71.6 km/s/Mpc

Abstract

Recent interest in New Early Dark Energy (NEDE), a cosmological model with a vacuum energy component decaying in a triggered phase transition around recombination, has been sparked by its impact on the Hubble tension. Previous constraints on the model parameters were derived in a Bayesian framework with Markov-chain Monte Carlo (MCMC) methods. In this work, we instead perform a frequentist analysis using the profile likelihood in order to assess the impact of prior volume effects on the constraints. We constrain the maximal fraction of NEDE $f_\mathrm{NEDE}$, finding $f_\mathrm{NEDE}=0.076^{+0.040}_{-0.035}$ at $68 \%$ CL with our baseline dataset and similar constraints using either data from SPT-3G, ACT or full-shape large-scale structure, showing a preference over $\Lambda$CDM even in the absence of a SH0ES prior on $H_0$. While this is stronger evidence for NEDE than obtained with the corresponding Bayesian analysis, our constraints broadly match those obtained by fixing the NEDE trigger mass. Including the SH0ES prior on $H_0$, we obtain $f_\mathrm{NEDE}=0.136^{+0.024}_{-0.026}$ at $68 \%$ CL. Furthermore, we compare NEDE with the Early Dark Energy (EDE) model, finding similar constraints on the maximal energy density fractions and $H_0$ in the two models. At $68 \%$ CL in the NEDE model, we find $H_0 = 69.56^{+1.16}_{-1.29} \text{ km s}^{-1}\text{ Mpc}^{-1}$ with our baseline and $H_0 = 71.62^{+0.78}_{-0.76} \text{ km s}^{-1}\text{ Mpc}^{-1}$ when including the SH0ES measurement of $H_0$, thus corroborating previous conclusions that the NEDE model provides a considerable alleviation of the $H_0$ tension.