Probing Departures from ΛCDM by Late-time Datasets

Abstract Observational data play a pivotal role in identifying cosmological models that are both theoretically consistent and empirically viable. In this work, we investigate the level of preference for dynamical dark energy over a cosmological constant using current late-time observational datasets, including cosmic chronometers (CC), baryon acoustic oscillations from Dark Energy Spectroscopic Instrument (DESI) DR2, and different Type Ia supernova catalogs (Pantheon + , DES-Dovekie, Union3). We analyze various dynamical dark-energy models, including ω CDM, o ω CDM, ω 0 ω a CDM, logarithmic, exponential, Jassal–Bagla–Padmanabhan (JBP), Barboza–Alcaniz (BA), and GEDE. In most cases, the oΛCDM and o ω CDM models favor an open Universe. For the o ω CDM, the inclusion of DES-Dovekie or Union3 data together with CC and DESI DR2 favors a nearly flat geometry. Using the CC + DESI DR2 dataset, the preference for dynamical dark energy lies between the 1 σ and 2 σ level. When different supernova catalogs (DES-Dovekie or Union3) are included, the deviation from ΛCDM in the ω CDM, ω 0 ω a CDM, logarithmic, JBP, BA, and GEDE models increases to the 2 σ –2.74 σ level, while the Pantheon + sample yields deviations below the 2 σ level. We find consistent evidence for ω 0 > −1 and ω a < 0 across all dark-energy models, indicating a preference for dynamical dark energy characterized by a Quintom-B-type scenario. The ΛCDM paradigm has long served as the standard framework of modern cosmology; however, recent DESI DR2 results have exposed emerging tensions with the cosmological constant Λ, hinting at possible new physics in the dark-energy sector. Even so, the currently available data are still not strong enough to definitively rule out the ΛCDM model.