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 ωCDM, oωCDM, ω0ωaCDM, logarithmic, exponential, Jassal–Bagla–Padmanabhan (JBP), Barboza– Alcaniz (BA), and GEDE. In most cases, the oΛCDM and oωCDM models favor an open Universe. For the oωCDM, 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 1σ and 2σ level. When different supernova catalogs (DES-Dovekie or Union3) are included, the deviation from ΛCDM in the ωCDM, ω0ωaCDM, logarithmic, JBP, BA, and GEDE models increases to the 2σ–2.74σ level, while the Pantheon+ sample yields deviations below the 2σ level. We find consistent evidence for ω0 > −1 and ωa < 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.