在低红移处发现5σ宇宙膨胀率矛盾，或暗示新物理存在。
A New $\sim 5σ$ Tension at Characteristic Redshift from DESI-DR1 BAO and DES-SN5YR Observations
- 用多任务高斯过程重建角直径距离，避免模型假设。
- 在z~0.512处测得的哈勃常数与ΛCDM预测偏差超5σ。
- 首次在低红移发现显著张力，适合关注宇宙学新物理者。
我们采用多任务高斯过程（MTGP）框架，基于DESI-DR1 BAO和DES-SN5YR数据集，对角直径距离（$D_A$）进行无模型重建，并将声学视界 $r_d$ 校准至普朗克最优值以确保早期宇宙物理一致性。在两个关键红移 $z\sim 1.63$（$D_A^\prime = 0$）和 $z\sim 0.512$（$D_A^\prime = D_A$）处重构 $D_A$，进而推导出宇宙膨胀率 $H(z)$。结果表明，在 $z\sim 1.63$ 处 $H(z)$ 与普朗克-2018 ΛCDM预测一致，未见新物理迹象；但在 $z\sim 0.512$ 处，$H(z)$ 与 ΛCDM 预测的偏差超过5σ，暗示普朗克-2018约束下的ΛCDM模型在低红移可能失效。这一新出现的~5σ张力不同于已有“哈勃张力”，或为低红移新物理的首例强证据。
原文摘要 · Abstract (English)
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.
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