Testing the direction of dark sector interaction using late-time datasets

Abstract

We constrain the phenomenological interacting dark energy (

IDE) model, in which the relative evolution of dark matter and dark energy is characterized by the scaling relation

$$\rho _\textrm{X}/\rho _m \propto a^{\xi }$$ ρ X / ρ m ∝ a ξ

, using baryon acoustic oscillation measurements from DESI Data Releases 1 and 2, combined with cosmic chronometers, compressed CMB likelihoods, and the Pantheon

$$^+$$ +

, DES-Dovekie, and Union3 Type Ia supernova samples. Parameter constraints are obtained using the cosmological inference code . Relative to

$$\Lambda $$ Λ

CDM, the

$$\xi $$ ξ

IDE model mildly favors higher values of the Hubble constant, reducing but not resolving the

$$H_0$$ H 0

tension. The parameter

$$\xi $$ ξ

remains close to its

$$\Lambda $$ Λ

CDM limit, while most dataset combinations favor

$$w_\textrm{X}>-1$$ w X > - 1

, indicating a mild preference for quintessence-like dark energy. The interaction combination

$$\xi +3w_\textrm{X}$$ ξ + 3 w X

is negative for all dataset combinations, corresponding to energy transfer from dark energy to dark matter. The strongest deviation from the non-interacting limit is obtained for CMB + DESI DR2 + CC + Union3, with

$$\xi +3w_\textrm{X}=-0.035\pm 0.023$$ ξ + 3 w X = - 0.035 ± 0.023

, corresponding to only

$$1.52\sigma $$ 1.52 σ

. Although the

$$N\sigma $$ N σ

statistic shows a weak preference for the interacting scenario, Bayesian evidence consistently favors

$$\Lambda $$ Λ

CDM. Overall, observations provide no compelling evidence for a nonzero dark-sector interaction, despite a consistent mild preference for energy transfer from dark energy to dark matter.