Testing the Direction of Dark Sector Interaction Using Late-Time Datasets

In this work, we constrain the phenomenological interacting dark energy xi IDE model using baryon acoustic oscillation measurements from DESI Data Release 1 and Data Release 2, combined with cosmic chronometer measurements, compressed CMB likelihoods, and three different Type Ia supernova compilations: Pantheon+, DES-Dovekie, and Union3. We constrain the parameters of the xi IDE model using a Markov Chain Monte Carlo analysis, using the nested sampling algorithm implemented in the dynesty package through the cosmological inference code SimpleMC. Compared to CDM, the xi IDE model favors slightly higher values of the Hubble constant, leading to a reduction in the Hubble tension. However, the tension is not completely resolved for any dataset combination. The parameter xi is consistently constrained to values close to its CDM prediction, indicating no statistically significant deviation from the standard cosmological scenario. Similarly, except for the CMB + DESI DR1 + CC dataset combination, the dark energy equation-of-state parameter prefers values of w X>-1, showing a preference for quintessence-like behavior and providing evidence for dynamical dark energy. The interaction parameter combination, xi+3w X, is found to be negative for all dataset combinations, corresponding to energy transfer from dark energy to dark matter. The strongest preference is obtained for the CMB + DESI DR2 + CC + Union3 dataset combination, yielding xi+3w X=-0.035 plus or minus0.023, which corresponds to a deviation of only 1.52 sigma from the non-interacting limit. Therefore, the current data provide only a weak indication of a non-zero dark-sector interaction. Model comparison based on the N sigma statistic shows weak evidence in favor of the interacting scenario, while Bayesian evidence consistently prefers the CDM model.