A New $\sim 5σ$ Tension at Characteristic Redshift from DESI-DR1 BAO and DES-SN5YR Observations

Abstract

We perform a model-independent reconstruction of the angular diameter distance ($D_{A}$) using the Multi-Task Gaussian Process (MTGP) framework with DESI-DR1 BAO and DES-SN5YR datasets. We calibrate the comoving sound horizon at the baryon drag epoch $r_d$ to the Planck best-fit value, ensuring consistency with early-universe physics. With the reconstructed $D_A$ at two key redshifts, $z\sim 1.63$ (where $D_{A}^{\prime} =0$) and at $z\sim 0.512$ (where $D_{A}^{\prime} = D_{A}$), we derive the expansion rate of the Universe $H(z)$ at these redshifts. Our findings reveal that at $z\sim 1.63$, the $H(z)$ is fully consistent with the Planck-2018 $Λ$CDM prediction, confirming no new physics at that redshift. However, at $z \sim 0.512$, the derived $H(z)$ shows a more than $5σ$ discrepancy with the Planck-2018 $Λ$CDM prediction, suggesting a possible breakdown of the $Λ$CDM model as constrained by Planck-2018 at this lower redshift. This emerging $\sim 5σ$ tension at $z\sim 0.512$, distinct from the existing ``Hubble Tension'', may signal the first strong evidence for new physics at low redshifts.

Figures (3)

• Figure 1: Reconstructed evolution for $D_A(z)$ and $D_A'(z)$ as a function of redshift, with RQ kernel. The shaded regions correspond to the 1$\sigma$ and 2$\sigma$ confidence levels. The two characteristic redshifts $z_1$ (where $D_A'(z_1)=0$) and $z_2$ ($D_A'(z_2)=D_A(z_2)$) are marked with circle and square markers. The Planck $\Lambda$CDM best-fit curves for $D_A(z)$ and $D_A'(z)$ are shown in dashed lines.
• Figure 2: Reconstruction of $D_A$ vs $z$. The DESY5 and DESI data points are shown for comparison. The reconstructed vales of $D_A(z_1)$ and $D_A(z_2)$ are marked for illustration.
• Figure 3: Residuals $\Delta H(z_1) \equiv H(z_1)^{\text{Reconstruction}} - H(z_1)^{\text{$\Lambda$CDM}}$ and $\Delta H(z_2) \equiv H(z_2)^{\text{Reconstruction}} - H(z_2)^{\text{$\Lambda$CDM}}$, assuming the RQ kernel for reconstruction.