Evolving and interacting dark energy: photometric and spectroscopic synergy with DES Y3 and DESI DR2 (2512.17684v1)

Abstract: We investigate the Dark Scattering (DS) interacting dark energy scenario, characterised by pure momentum exchange between dark matter and dark energy, allowing for a time-dependent equation-of-state described by the Chevallier-Polarski-Linder (CPL) parametrisation. This class of models is weakly constrained by CMB observations and can exhibit distinctive late-time suppression of structure growth. We derive constraints on cosmological, DS, and CPL parameters using three two-point correlation functions from the Dark Energy Survey Year 3 data, combined with baryon acoustic oscillation measurements from DESI, Type Ia supernovae from DES Year 5, and CMB data from Planck. We find the dark-sector interaction parameter $A_\mathrm{ds}$ to be consistent with zero for all data combinations, and that CPL provides a statistically preferred fit over DS for the selected probes. From the full data combination we obtain $w_0=-0.76\pm0.06, \, w_a=-0.77^{+0.23}_{-0.20}$ for CPL, and $w_0=-0.79^{+0.05}_{-0.06}, \, w_a=-0.56^{+0.24}_{-0.15}, \, (A_\mathrm{ds}=9.8^{+2.8}_{-9.5}\,\mathrm{bn/GeV} )$ for DS. The inclusion of DES photometric information improves the Figure-of-Merit on $(w_0,w_a)$ by $\sim$20% for CPL and $\sim$50% for DS relative to DESI+SN+CMB alone. We find no evidence for an $S_8$ discrepancy in either model. These results provide the most stringent pre-Euclid constraints on DS from a combined photometric and spectroscopic analysis.