Does DESI 2024 confirm ΛCDM?

Abstract

We demonstrate that a $\sim 2\sigma$ discrepancy with the Planck-ΛCDM cosmology in DESI Luminous Red Galaxy (LRG) data in the redshift range $0.4<z<0.6$ with effective redshift $z_{\text{eff}}=0.51$ translates into an unexpectedly large ${\Omega }_m$ value, ${\Omega }_m={0.67}_{-0.17}^{+0.18}$. We independently confirm that this anomaly drives the preference for $w_0>-1$ in DESI data alone confronted to the $w_0{w}_a$CDM model. Given that LRG data at $z_{\text{eff}}=0.51$ is at odds with Type Ia supernovae in overlapping redshifts, we expect that this anomaly will decrease in statistical significance with future DESI data releases leaving an increasing ${\Omega }_m$ trend with effective redshift at higher redshifts. We estimate the current significance of the latter in DESI data at $\sim 1.8\sigma$ and comment on how it dovetails with independent observations. It is imperative to understand what makes DESI LRG data at $z_{\text{eff}}=0.51$ an outlier when it comes to ${\Omega }_m$ determinations.