Does DESI DR2 challenge $Λ$CDM paradigm ? (2507.21607v1)

Abstract: Although the debate about the systematic errors of DESI DR1 is still open, recent DESI DR2 is consistent with DESI DR1 and further strengthens the results of DESI DR1. In this analysis, we present a $\sim 2.38 \sigma$ discrepancy between Planck $\Lambda$ CDM cosmology and the DESI DR2 Luminous Red Galaxy (LRG1) data at $z_{\text{eff}} = 0.51$, which predicts an unexpectedly large value for $\Omega_m$, $\Omega_m = 0.471^{+0.119}_{-0.065}$. We find that the $w_0 w_a$CDM model, using DESI DR2 data, suggests $w_0 > 1$, indicating a deviation from the standard $\Lambda$CDM paradigm, where is strictly $w_0 = -1$. Additionally, the DESI DR2 data reveals that the value of $\Omega_m$ fluctuates at the 2.97 $\sigma$ level as redshift bin increases, particularly within the $\Lambda$CDM paradigm. The DESI DR2 LRG1 data at $z_{\text{eff}} = 0.51$ seem to contradict the results from Type Ia supernovae in the same redshift range. However, it is expected that this discrepancy will become less significant with future DESI data releases, and the trend for $\Omega_m$ is expected to continue to increase as higher redshifts are considered. The statistical significance of this trend was approximately $1.8 \sigma$ when only the DESI DR1 data was considered, but, in the light of DESI DR2 data, the significance has decreased to about $0.52 \sigma$. Despite this reduction, the trend showing an increase in $\Omega_m$ with higher redshifts remains, though with less statistical confidence. This highlights the importance of understanding why the DESI LRG1 data at $z_{\text{eff}} = 0.51$ appear to be an outlier in the determination of $\Omega_m$.