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

Deng Wang, Olga Mena, Salvatore Capozziello, David Mota

TL;DR

The paper investigates cosmic curvature by combining low-redshift distance probes (DESI BAO and SN Ia) with high-redshift CMB data. It finds that low-redshift observations consistently prefer an open universe, while Planck CMB data favor negative curvature; including DESI shifts the overall preference toward $\Omega_k>0$, with the significance strengthening to above $3\sigma$ in some combinations and up to $5\sigma$ for DESY5 SN Ia data with a $\theta_*$ prior. This curvature tension between early- and late-universe observations persists under various priors and SN Ia datasets, suggesting physics beyond the minimal $\Lambda$CDM and posing a potential challenge to standard inflationary predictions. The work highlights the importance of cross-validating curvature constraints with diverse datasets and motivates improved future measurements to resolve the tension and its implications for inflation and open-inflation models.

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 $\sim 2σ$ 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 $2σ$ evidence for an open universe, regardless of the SN Ia sample employed. When considering DESI, SN Ia and the acoustic scale $θ_\star$ data, the preference for an open universe exceeds the $3σ$ level, reaching $5σ$ 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 $Λ$CDM scheme, thereby challenging the standard inflationary predictions.

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

TL;DR

The paper investigates cosmic curvature by combining low-redshift distance probes (DESI BAO and SN Ia) with high-redshift CMB data. It finds that low-redshift observations consistently prefer an open universe, while Planck CMB data favor negative curvature; including DESI shifts the overall preference toward , with the significance strengthening to above in some combinations and up to for DESY5 SN Ia data with a prior. This curvature tension between early- and late-universe observations persists under various priors and SN Ia datasets, suggesting physics beyond the minimal CDM and posing a potential challenge to standard inflationary predictions. The work highlights the importance of cross-validating curvature constraints with diverse datasets and motivates improved future measurements to resolve the tension and its implications for inflation and open-inflation models.

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 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 evidence for an open universe, regardless of the SN Ia sample employed. When considering DESI, SN Ia and the acoustic scale data, the preference for an open universe exceeds the level, reaching 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 CDM scheme, thereby challenging the standard inflationary predictions.
Paper Structure (5 sections, 2 equations, 2 figures, 1 table)

This paper contains 5 sections, 2 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Basics
  3. Data and Methods
  4. Results
  5. Discussions and conclusions

Figures (2)

  • Figure 1: Left panel: one-dimensional probability distributions of the curvature parameter from high-redshift probes such as CMB, Planck and from each low-redshift probe considered here independently. Right panel: two-dimensional allowed contours at the 68% and 95% CL in the ($\Omega_k$, $\Omega_m$) plane from CMB and from CMB plus a number of different cosmological low-redshift probes.
  • Figure 2: One-dimensional probability distributions for CMB, Planck and DESI, plus the former combined with different Supernovae Ia luminosity distance datasets (Pantheon+, Union3 or DESY5) and/or BBN/angular diameter distance priors.