Constraints on Coupled Dark Energy in the DESI Era

TL;DR

This study tests coupled dark energy models against current cosmological data, finding a slight preference for a small coupling parameter and demonstrating the model's ability to explain phantom divide crossing.

Contribution

It provides the first comprehensive analysis of coupled dark energy with both flat and Peebles-Ratra potentials using recent datasets, assessing asymmetries and robustness.

Findings

Excludes no-coupling scenario at 95% CL.

Finds a peak at |2|0.03 for the coupling parameter.

Model can explain crossing of the phantom divide within 2 confidence.

Abstract

WWe investigate the current viability of a well-known coupled dark energy scenario in which cold dark matter (DM) interacts with a spin-0 dark energy component through a non-trivial field dependence of the DM mass. This ultra-light scalar mediates a fifth force between DM particles, which can leave signatures on cosmological scales. We use state-of-the-art data on the cosmic microwave background from Planck's CamSpec likelihood, baryon acoustic oscillations from the second DESI data release as well as the supernovae of Type Ia (SNIa) from Pantheon+ and DES-Dovekie. We perform the analysis considering both a flat potential and a Peebles-Ratra (PR) potential for the scalar field in order to assess the impact of the potential slope on the fitting performance of the model. While for a constant potential the scalar field dynamics is insensitive to the sign of the coupling parameter $\beta$, the PR potential breaks the existing symmetry in the solutions at late times and could induce a difference at the phenomenological level between positive and negative values. We study for the first time if it is actually the case, finding no important asymmetry in the fitting results. In the light of the aforesaid datasets, we find in all cases a peak at $|\beta|\sim 0.03$ - less pronounced than reported in some recent works -, excluding the no-coupling scenario at $\sim 95\%$ CL. The model is able to explain an effective crossing of the phantom divide, with the equation-of-state parameter lying within the $2\sigma$ bands of model-agnostic reconstructions. Our results are very robust under changes in the SNIa sample used in the analysis and is not significantly altered when we replace a constant potential with the PR one, although the latter is crucial to produce the aforesaid crossing. In passing, we also provide constraints obtained with the PR potential in the uncoupled case.