Model-independent cosmological inference post DESI DR1 BAO measurements

TL;DR

The paper tackles cosmological inferences under minimal model assumptions by applying Gaussian process regression to reconstruct the expansion history from Pantheon-Plus SN-Ia data and BAO measurements (SDSS-IV and DESI DR1). It assesses ΛCDM viability and dark-energy dynamics through $H(z)$, the Om diagnostic, and the total equation of state $w_{tot}$, across multiple SN-Ia datasets (including DES-5YR and Union3) and BAO combinations. Results generally place ΛCDM within 2σ, but show dataset-dependent tensions: some combinations hint quintessence-like behavior and possible phantom crossing, while others keep ΛCDM within 1σ; notable tensions in $H_0 r_d$ persist between certain SN-BAO pairings. The analysis demonstrates the value and limitations of model-independent, data-driven cosmological inference and motivates further exploration with alternative ML approaches and expanded datasets.

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 $Λ$CDM model is always included in the 95\% confidence intervals. We find evidence that the DESI LRG data at $z_{\text{eff}} = 0.51$ 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 towards 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 data sets predicts that the $Λ$CDM model lies outside the 3$σ$ confidence levels, whereas with DESI BAO + Union3 data, the $Λ$CDM model is always included within 1$σ$. We also report constraints on $H_0 r_d$ from our model-agnostic analysis, independent of the pre-recombination physics. Our results point towards an $\approx$ 2$σ$ discrepancy between the DESI + Pantheon-Plus and DESI + DES-5YR data sets, which calls for further investigation.

Figures (21)

• Figure 3: Plots for mean values of the reconstructed functions $\mathcal{O}m$ (left) and $w_{\text{tot}}$ (right) along with the 1$\sigma$, 2$\sigma$ and 3$\sigma$ uncertainties for the DESI BAO no-LRG1 + Pantheon-Plus SN data sets.
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