Measuring cosmic curvature with non-CMB observations

The cosmic curvature $\Omega_{K}$ is an important parameter related to the inflationary cosmology and the ultimate fate of the universe. In this work, we adopt the non-CMB observations to constrain $\Omega_{K}$ in the $\Lambda$CDM model and its extensions. The DESI baryon acoustic oscillation, DES type Ia supernova, cosmic chronometer, and strong gravitational lensing time delay data are considered. We find that the data combination favors an open universe in the $\Lambda$CDM model, specifically $\Omega_{K}=0.108\pm0.056$ at the $1\sigma$ confidence level, which is in $2.6\sigma$ tension with the Planck CMB result supporting our universe being slightly closed. In the $\Lambda$CDM extensions, the data combination is consistent with a spatially flat universe. However, the central value of $\Omega_{K}$ is positive and has a significant deviation from zero. We adopt the Akaike information criterion to compare different cosmological models. The result shows that non-flat models fit the observational data better than the flat $\Lambda$CDM model, which adds evidence to the argument that flat $\Lambda$CDM is not the ultimate model of cosmology.