Constraints on the Modified Emergent Dark Energy Model Using DESI DR2 BAO

Abstract

In this work, we investigate the modified emergent dark energy (MEDE) model using baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2), together with CMB information from the {\tt LoLLiPoP} (low-$\ell$) and {\tt HiLLiPoP} (high-$\ell$) likelihoods based on the latest Planck NPIPE PR4 release, Planck PR4 lensing, ACT DR6 lensing, and three Type Ia supernova samples (Pantheon$+$, DES-Dovekie, and Union3). We find that the MEDE model remains largely consistent with the standard $\Lambda$CDM cosmology. Although small departures from $\Lambda$CDM are allowed, the inclusion of SNe~Ia data drives the model parameters toward the standard cosmological scenario, with the parameter $\alpha$ remaining consistent with $\alpha=0$ at the $1\sigma$ level. The model does not significantly alleviate the $H_0$ or $S_8$ tensions: the inferred $H_0$ values remain below the SH0ES measurement, the sound horizon $r_d$ is nearly unchanged, and the predicted $S_8$ values remain close to those of $\Lambda$CDM. The reconstructed cosmological evolution closely follows the $\Lambda$CDM prediction, with deviations generally below the $0.5\sigma$ level. While the CMB + DESI DR2 dataset favors a full phantom regime, the inclusion of SNe~Ia shifts the evolution toward a full quintessence regime. Finally, although the $\Delta\chi^2_{\rm MAP}$ and $\Delta{\rm AIC}$ criteria indicate a marginally better fit than $\Lambda$CDM, the logarithmic Bayes factor provides only inconclusive evidence in favor of the MEDE model. Overall, the MEDE model remains compatible with current observations but does not exhibit the phantom-crossing behavior suggested by recent DESI DR2 analyses.