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 being a mere cosmological constant $\Lambda$. 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 confronting 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 (EoS) evolves from $w>-1$ at early times to $w<-1$ at late times, while DESI+DESY5 exhibits a distinct preference for quintessence where $w>-1$ across cosmic evolution. The joint analysis yields constraints that align more closely with the ACT preference. Critically, the canonical RDE model fails to provide a coherent description of cosmic evolution, as it manifests severe tensions (even exceeding $10\sigma$ significance) between early- and late-universe parameter reconstructions. Based on the combined data, Bayesian evidence decisively disfavors both HDE and RDE models relative to the $\Lambda$ cold dark matter model, with ACT providing decisive disfavor and DESI+DESY5 yielding moderate disfavor. Our results show that the HDE and RDE models remain excluded by the new data, reinforcing earlier conclusions drawn from previous datasets.