Probing Dark Energy Evolution Post-DESI 2024

Abstract: We study the evidence for dark energy (DE) evolution at low redshift, using baryonic acoustic oscillations (BAOs) from the DESI Early Data Release, Pantheon+ Type Ia supernovae (SNe-Ia), and redshift space distortions (RSDs) to constrain cosmological parameters. Furthermore, we make use of the angular acoustic scale to analyse the effect of introducing condensed CMB information on the cosmological parameters informing DE evolution. The analysis is divided into cases based on the variability of priors inferred from early-time physics. Using a quadratic parametrisation, $X(z)$, for DE density, we find evidence for DE evolution in all cases, both with and without the angular acoustic scale. We reconstruct $X(z)$ using best fit parameters and find that DE density starts to exhibit dynamical behaviour at $z \sim 0.5 $, assuming negative values beyond $z\sim 1.5$. The data show no significant preference for $X(z)$CDM over a $\Lambda$CDM, with both models performing equally well according to our chosen metrics of reduced $\chi^2$ and the Durbin-Watson statistic.