Is there evidence for CIDER in the Universe?

TL;DR

This paper investigates the linear behavior of the constrained interacting dark energy (CIDER) model, analyzing its cosmological predictions and compatibility with observational data, revealing enhanced matter perturbations and potential alleviation of the  tension.

Contribution

It provides a detailed analysis of the CIDER model's linear cosmological behavior, including subtleties of background evolution and effects on matter perturbations, with new insights into its observational viability.

Findings

Matter perturbations are enhanced at large scales compared to CDM.

The coupling parameter can alleviate the  tension.

Planck data favors the CDM limit of the model.

Abstract

In this work we analyze the full linear behaviour of the constrained interacting dark energy (CIDER) model, which is a conformally coupled quintessence model tailored to mimic a $\Lambda$CDM expansion. We compute the matter and temperature anisotropies power spectra and test the model against recent observational data. We shed light on some particular subtleties of the background behaviour that were not fully captured in previous works, and study the physics of the linear cosmological observables. One novelty found was that matter perturbations are enhanced at large scales when compared with the ones of the standard $\Lambda$CDM. The reason and impact of this trend on the cosmological observables and on the physics of the early Universe are considered. We find that the introduction of the coupling parameter alleviates the $\sigma_8$ tension between early and late time probes although Planck data favours the $\Lambda$CDM limit of the model.