A New $\sim 5\ddot{I}ƒ$ 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 $\hat{I}›$CDM prediction, confirming no new physics at that redshift. However, at $z\sim 0.512$, the derived $H(z)$ shows a more than $5\ddot{I}ƒ$ discrepancy with the Planck-2018 $\hat{I}›$CDM prediction, suggesting a possible breakdown of the $\hat{I}›$CDM model as constrained by Planck-2018 at this lower redshift. This emerging $\sim 5\ddot{I}ƒ$ tension at $z\sim 0.512$, distinct from the existing ``Hubble Tension'', may signal the first strong evidence for new physics at low redshifts.

4 pages, 1 table, 3 figures. Comments are welcome. New References added