Does DESI 2024 Confirm $\Lambda$CDM?

TL;DR

This paper investigates a notable discrepancy in DESI LRG data at redshift 0.51, which suggests a higher matter density parameter, potentially impacting cosmological model preferences and highlighting the need for further analysis of this outlier.

Contribution

The study identifies and characterizes an anomaly in DESI LRG data at z=0.51, exploring its implications for cosmological parameters and model preferences compared to previous observations.

Findings

DESI LRG data at z=0.51 shows a 2 sigma discrepancy with Planck-$cdm$.

This anomaly influences the preference for $w_0 > -1$ in DESI data.

The anomaly's significance is estimated at about 1.8 sigma and may decrease with future data.

Abstract

We demonstrate that a $\sim 2 \sigma$ discrepancy with the Planck-$\Lambda$CDM cosmology in DESI Luminous Red Galaxy (LRG) data in the redshift range $0.4 < z < 0.6$ with effective redshift $z_{\textrm{eff}} = 0.51$ translates into an unexpectedly large $\Omega_m$ value, $\Omega_m = 0.67^{+0.18}_{-0.17}$. We independently confirm that this anomaly drives the preference for $w_0 > -1$ in DESI data \textit{alone} confronted to the $w_0 w_a$CDM model. Given that LRG data at $z_{\textrm{eff}} = 0.51$ 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 $z_{\textrm{eff}} = 0.51$ an outlier when it comes to $\Omega_m$ determinations.