Non-minimal dark sector physics and cosmological tensions

TL;DR

This paper investigates non-minimal dark sector models, including interactions and varying dark energy equations of state, to address cosmological tensions like the Hubble constant discrepancy, analyzing their statistical significance and compatibility with observational data.

Contribution

It provides a comprehensive analysis of extended dark energy models, highlighting their potential to alleviate cosmological tensions and assessing their statistical support with current observational datasets.

Findings

Coupled quintessence models show >5σ evidence for dark sector interaction.

All models considered raise the Hubble constant, easing the H0 tension.

Bayesian evidence mildly favors coupled vacuum models over others.

Abstract

We explore whether non-standard dark sector physics might be required to solve the existing cosmological tensions. The properties we consider in combination are an interaction between the dark matter and dark energy components, and a dark energy equation of state $w$ different from that of the canonical cosmological constant $w=-1$. In principle, these two parameters are independent. In practice, to avoid early-time, superhorizon instabilities, their allowed parameter spaces are correlated. We analyze three classes of extended interacting dark energy models in light of the 2019 Planck CMB results and Cepheid-calibrated local distance ladder $H_0$ measurements of Riess et al. (R19), as well as recent BAO and SNeIa distance data. We find that in quintessence coupled dark energy models, where $w > -1$, the evidence for a non-zero coupling between the two dark sectors can surpass the $5\sigma$ significance. On the other hand, in phantom coupled dark energy models, there is no such preference for a non-zero dark sector coupling. All the models we consider significantly raise the value of the Hubble constant easing the $H_0$ tension. The addition of low-redshift BAO and SNeIa measurements leaves some residual tension with R19 but at a level that could be justified by a statistical fluctuation. Bayesian evidence considerations mildly disfavour both the coupled quintessence and phantom models, while mildly favouring a coupled vacuum scenario, even when late-time datasets are considered. We conclude that non-minimal dark energy cosmologies, such as coupled quintessence, phantom, or vacuum models, are still an interesting route towards softening existing cosmological tensions, even when low-redshift datasets and Bayesian evidence considerations are taken into account. (abstract severely abridged)