Model-independent cosmological inference post DESI DR1 BAO measurements

Abstract

In this work, we implement Gaussian process regression to reconstruct the expansion history of the Universe in a model-agnostic manner, using the Pantheon-Plus SN-Ia compilation in combination with two different BAO measurements (SDSS-IV and DESI DR1). In both the reconstructions, the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model is always included in the 95% confidence levels. We find evidence that the DESI LRG data at ${z}_{\mathrm{eff}}=0.51$ is not an outlier within our model-independent framework. We study the $\mathcal{O}m$ diagnostics and the evolution of the total equation of state (EOS) of our Universe, which hint toward the possibility of a quintessence-like dark energy scenario with a very slowly varying EOS and a phantom crossing in higher $z$. The entire exercise is later complemented by considering two more SN-Ia compilations---DES-5YR and Union3---in combination with DESI BAO. Reconstruction with the DESI BAO + DES-5YR SN datasets predicts that the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model lies outside the $3\ensuremath{\sigma}$ confidence intervals, whereas with DESI BAO + Union3 data, the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model is always included within $1\ensuremath{\sigma}$. We also report constraints on ${H}_{0}{r}_{d}$ from our model-agnostic analysis, independent of the pre-recombination physics. Our results point toward an $\ensuremath{\approx}2\ensuremath{\sigma}$ discrepancy between the DESI + Pantheon-Plus and DESI + DES-5YR datasets, which calls for further investigation.

Topics & Concepts