Braneworld dark energy in light of DESI DR2

Abstract

Recent observational results from the DESI collaboration reveal tensions with the standard ΛCDM model and favour a scenario in which dark energy (DE) decays over time. The DESI DR2 data also suggest that the DE equation of state (EoS) may have been phantom-like (w < -1) in the past, evolving to w > -1 at present — implying a recent crossing of the phantom divide at w = -1. Scalar field models of DE naturally emerge in ultraviolet-complete theories such as string theory, which is typically formulated in higher dimensions. In this work, we investigate a broad class of thawing scalar field models — including the simple quadratic, quartic, exponential, symmetry-breaking and axion potentials — propagating on a (4+1)-dimensional ghost-free phantom braneworld, and demonstrate that their effective EoS exhibits a phantom-divide crossing. Alongside the Hubble parameter and EoS of DE, we also analyse the evolution of the Om diagnostic, and demonstrate that the time dependence of these quantities is in excellent agreement with the DESI DR2 observations. Furthermore, we perform a comprehensive parameter estimation using Markov Chain Monte Carlo sampling, and find that the χ^2 values for all our models are remarkably close to that of the widely used CPL parametrisation — indicating that our models fit the data very well.