Confronting Cold New Early Dark Energy and its Equation of State with Updated CMB, Supernovae, and BAO Data

TL;DR

This study constrains Cold NEDE, a model addressing the Hubble tension, using recent CMB, BAO, and supernovae data, and explores an extended version with evolving equation of state, showing promising tension reduction.

Contribution

It introduces an extended Cold NEDE fluid model with a dynamic equation of state and tests its compatibility with new cosmological datasets, improving tension mitigation.

Findings

Data favors a simple time dependence of the NEDE equation of state.

The model reduces the Hubble tension from 6.3σ to 2.6σ with new BAO data.

The extended model slightly improves the fit compared to the base model.

Abstract

Cold New Early Dark Energy (Cold NEDE) addresses the Hubble tension through a triggered vacuum phase transition in the dark sector. In this paper, we constrain a phenomenological fluid model using recent cosmic microwave background likelihoods based on Planck NPIPE data alongside baryonic acoustic oscillations (BAO) and supernovae data from Pantheon+. Exploiting the enhanced constraining power of the datasets, we introduce and study an extended version of the NEDE fluid model in which the equation of state parameter $w_\mathrm{NEDE}$, characterizing the post-phase transition fluid, is allowed to evolve with non-vanishing derivatives ${d}w_\mathrm{NEDE}/d\ln a$ and ${d^2}w_\mathrm{NEDE}/{d}(\ln a)^2$. Our results indicate that data is compatible with a rather simple time dependence that could arise from a mixture of radiation and a stiff fluid. With the updated datasets, the base and extended models still show a significant reduction of the DMAP tension from $6.3 \sigma$ in $\Lambda$CDM down to $3.5\sigma$ with a small simultaneous reduction of the $S_8$ tension, slightly improving over recent findings for the axion-like early dark energy model. Finally, we also provide a first test of the model against new BAO data from the Dark Energy Spectroscopic Instrument (DESI) survey. Replacing the previous BAO constraints in our analysis with the new ones, the tension is further reduced to $2.6 \sigma$, reaffirming the Cold NEDE model as a promising solution to the Hubble tension.