Strong Evidence for Dark Sector Interactions

TL;DR

Recent cosmological data deviations from $\\Lambda$CDM are better explained by dark matter-dark energy interactions than by dynamical dark energy, with strong statistical evidence supporting IDE models as a viable alternative.

Contribution

This study provides the first comprehensive analysis of dark sector interactions using multiple datasets, demonstrating their statistical preference over dynamical dark energy models.

Findings

IDE models show 3-5$\sigma$ evidence for non-zero interactions.

IDE fits are comparable or superior to CPL dynamical DE models.

Results remain robust under SN recalibration, favoring IDE over dynamical DE.

Abstract

Recent DESI baryon acoustic oscillation data reveal deviations from $\Lambda$CDM cosmology, conventionally attributed to dynamical dark energy (DE). We demonstrate that these deviations are equally, if not better, explained by interactions between dark matter and dark energy (IDE), without requiring a time-varying DE equation of state. Using a unified framework, we analyze two IDE models -- coupled quintessence and coupled fluid -- against the latest CMB (Planck, ACT, SPT), DESI BAO, and SN (including DES-Dovekie recalibrated) data. Both IDE scenarios show robust evidence for non-vanishing interactions at the 3-5$\sigma$ level, with marginalized constraints significantly deviating from the $\Lambda$CDM limit. This preference persists even under DES-Dovekie SN recalibration, which weakens dynamical DE evidence. Crucially, for the same number of free parameters, IDE models provide fits to low- and high-redshift data that match or exceed the performance of the CPL dynamical DE parametrization. Our results establish IDE as a physically motivated alternative to dynamical DE, highlighting the necessity of future cosmological perturbation measurements (e.g., weak lensing, galaxy clustering) to distinguish between these paradigms.