Do low-redshift observations open the doors to an open universe?

TL;DR

Low-redshift observations of BAO and SN Ia suggest an open universe, conflicting with high-redshift CMB data, indicating a potential tension in cosmological models and challenging inflationary predictions.

Contribution

This study provides new evidence from low-redshift data favoring an open universe, contrasting with previous high-redshift results and highlighting a tension in cosmological observations.

Findings

Low-redshift data indicate an open universe at over 2σ significance.

The preference for an open universe exceeds 3σ when combining DESI, SN Ia, and acoustic scale data.

The results challenge standard inflationary models and suggest a tension between high- and low-redshift observations.

Abstract

The detection of a significant deviation from a zero curvature would have profound consequences for inflationary theories and fundamental physics. Relative to high-redshift Planck's CMB measurements, indicating a $\sim 2\sigma$ evidence for a closed universe, low-redshift observations of BAO and SN Ia have the advantages of weak dependence on early universe physics, independently observational systematics, and strong redshift dependence of distances in constraining the cosmic curvature. Using the integrated observations from DESI BAO and SN Ia, we find an unexpected $2\sigma$ evidence for an open universe, regardless of the SN Ia sample employed. When considering DESI, SN Ia and the acoustic scale $\theta_\star$ data, the preference for an open universe exceeds the $3\sigma$ level, reaching $5\sigma$ for the case of DESY5 Supernovae data. Therefore, low-redshift observations favor an open universe, and this preference persists even when alternative high-redshift priors are adopted. Our results point to the existence of an additional tension between high- and low-redshift observations, present also in non-flat models beyond the minimal $\Lambda$CDM scheme, thereby challenging the standard inflationary predictions.