Observational challenges to holographic and Ricci dark energy paradigms: Insights from ACT DR6 and DESI DR2*

Abstract Recent studies suggest that dark energy may be dynamical rather than a mere cosmological constant Λ. In this work, we examine the viability of two physically well-motivated dynamical dark energy models—holographic dark energy (HDE) and Ricci dark energy (RDE)—by validating them with the latest observational data, including ACT cosmic microwave background anisotropies, DESI baryon acoustic oscillations, and DESY5 supernovae. Our analysis reveals a fundamental tension between early- and late-universe constraints within both frameworks: ACT favors a quintom scenario where the dark energy equation of state evolves from at early times to at late times, whereas DESI+DESY5 exhibits a distinct preference for quintessence where across cosmic evolution. The RDE model fails to provide a coherent description of cosmic evolution, as it manifests severe tensions (exceeding significance) between early- and late-universe parameter reconstructions. Additionally, Bayesian evidence favors the ΛCDM model over both the aforementioned models. Our findings statistically exclude the original HDE and RDE models and uncover a severe discrepancy between early- and late-universe observations described by them, leading to the conclusion that the HDE and RDE models can be rejected based on current observational data.