Compartmentalization in the dark sector of the universe after DESI DR2 BAO data

Abstract

We study a non-linear interaction between the dark matter and dark energy components of the universe. Within a spatially flat FLRW geometry, dark matter is described by a dust fluid and dark energy by an ideal gas with a constant equation-of-state parameter, allowing for energy transfer between the two sectors. The resulting effective fluid leads to a unified dynamical dark energy model in which the Hubble function admits an analytic expression. We constrain this model using the DESI DR2 Baryon Acoustic Oscillation (BAO) measurements and the Pantheon+ Type Ia supernovae (SNe Ia) compilation. For the combined dataset, the interacting model provides a better fit than $\Lambda$CDM, with ${\chi }_{\mathrm{Interaction}}^2-{\chi }_{\Lambda \mathrm{CDM}}^2=-5$. Using the Akaike Information Criterion (AIC), we find ${\text{AIC}}_{\mathrm{Interaction}}-{\text{AIC}}_{\Lambda \mathrm{CDM}}=-1$, indicating that the interacting model is weakly preferred, though the difference is not statistically significant and disappears when considering BAO data alone. Finally, when comparing the interaction with the $w_0{w}_a$CDM (CPL) model, we find a small preference for the interaction in the BAO-only case, with ${\text{AIC}}_{\mathrm{Interaction}}-{\text{AIC}}_{w_0{w}_a}=-1.5$.