Sign-Switching Dark Energy: Smooth Transitions with Recent DESI DR2 Observations

TL;DR

Sign-switching dark energy models, which change sign at a certain redshift, can better fit recent cosmological data and help resolve the Hubble tension without complex new physics.

Contribution

This work introduces and tests a class of background-level cosmological models with sign-changing dark energy using recent observational data.

Findings

Sign-switching models alleviate the Hubble tension.

Models show better statistical fit than standard $\\Lambda$CDM.

Improved Hubble constant inference suggests a promising resolution to late-universe discrepancies.

Abstract

Sign-switching dark energy provides a novel mechanism for modifying the late-time expansion history of the Universe without invoking additional fields or finely tuned initial conditions. In this work, we investigate a class of background--level cosmological models in which the dark energy contribution changes sign at a transition redshift $z_\dagger$, producing a sharp deviation from standard $\Lambda$CDM dynamics. We confront these models with a comprehensive set of cosmological observations, including Planck 18 cosmic microwave background (CMB) measurements, DESI DR2 Baryonic Acoustic Oscillation (BAO) data and the Pantheon+ $\&$ SH0ES Type Ia supernova sample (SN). Using a full Markov Chain Monte Carlo (MCMC) analysis, we find that the sign-switching scenario significantly alleviates the Hubble tension while obtaining better results when statistically comparing with $\Lambda$CDM, as quantified by the Akaike and Bayesian information Criteria. Although the model is explored only at the background level, the improvement in the inferred Hubble constant demonstrates that sign-switching dark energy offers a promising and physically economical pathway toward resolving late-universe discrepancies.