Dark Energy in the DESI Era: A Brief Review of Evidence, Beyond-ΛCDM Interpretations, and Tensions

Abstract Recent baryon acoustic oscillation measurements from Dark Energy Spectroscopic Instrument (DESI) provide important new clues for reassessing whether the standard ΛCDM model offers a sufficient description of the late-time expansion history of the universe. When combined with cosmic microwave background and type Ia supernova data, these measurements show an apparent departure from the ΛCDM model, commonly described as dynamical dark energy (DDE) with equation of state crossing the phantom divide (i.e., quintom behavior). This review examines the current status of the DESI-motivated indications for DDE and their possible implications for physics beyond ΛCDM. We discuss how the strength of the preference for DDE depends on the adopted parametrization and data set combination, and how residual systematics or internal tensions among data sets may affect its interpretation. At the background level, several mechanisms beyond ΛCDM can produce similar expansion histories. We therefore further discuss how the same effective departure from w = −1 may arise from physically distinct scenarios, including interacting dark energy, non-minimally coupled gravity, and non-standard dark matter. Meanwhile, these different new-physics interpretations may have different implications for current cosmological tensions, especially those involving H 0 , S 8 , and ∑ m ν . In conclusion, the question posed by DESI is not merely whether dark energy evolves with time, but rather how, within the framework of precision cosmology, to disentangle new physics scenarios from systematic errors.