Probing Generalized Emergent Dark Energy with DESI DR2 (2507.00835v1)

Abstract: As an update on the initial findings of DESI, the new results provide the first hint of potential deviations from a cosmological constant ($w=-1$), which, if confirmed with significance $>5\sigma$, will falsify the $\Lambda$CDM model. We consider a novel generalised form of an emergent dark energy model and confront this through various data sets (Baryon Acoustic Oscillation (BAO) data from Dark Energy Spectroscopic Instrument Data Release (DESI DR2), Type Ia Supernovae (SNe Ia) compilation, and Cosmic Microwave Background (CMB) distance priors) and simultaneously constrain the dark energy (DE) equation of state and energy density $f_{DE}(z)$. The results for the joint posteriors of cosmological parameters and the reconstructed dark energy EoS $w(z)$ with the energy density $f_{DE}(z)$ for various combinations of data sets are discussed, which favors quintessence nature. Specifically, $w(0) = -0.820$ with DESI DR2 + CMB, $-0.845$ with DESI DR2 + CMB + PP$^+$, $-0.828$ with DESI DR2 + CMB + Union3, and $-0.804$ with DESI DR2 + CMB + DESY5. We adopted a novel method to probe shifts in the generalized emergent dark energy (GEDE) parameter ($\Delta$) by mapping 2D marginalized posterior distributions in the $\Delta-\Omega_{m0}$ plane. Our analysis consistently reveals a preference for negative $\Delta$ across multiple combinations of observational datasets. Incorporating these values into the matter power spectrum further supports the GEDE framework's viability. We quantify the model's performance using the Bayes factor.