Hubble tension tomography: BAO vs SnIa distance tension

TL;DR

This study probes the redshift dependence of the Hubble tension by directly comparing BAO distances calibrated via the CMB sound horizon to Cepheid-calibrated Pantheon+ SnIa distances, using redshift tomography across 13 bins and an up-to-date BAO dataset including DESI. The analysis reveals a pronounced tension at low redshift (z~0.1–0.8) that weakens at higher redshift (z~0.8–2.3), suggesting that calibrator differences dominate the discrepancy and that simple H(z) deformations cannot fully reconcile the data. Tests of late- and high-redshift H(z) deformation models (notably Λ_sCDM) improve fits in some regimes but still struggle to fit BAO and SnIa data simultaneously across all redshifts. Overall, the results underscore the need to re-evaluate distance calibrations and consider potential high-z deviations from Planck18/ΛCDM, while highlighting the persistent nature of the Hubble tension.

Abstract

We investigate the redshift dependence of the Hubble tension by comparing the luminosity distances obtained using an up-to-date BAO dataset (including the latest DESI data) calibrated with the CMB-inferred sound horizon, and the Pantheon+ SnIa distances calibrated with Cepheids. Using a redshift tomography method, we find: 1) The BAO-inferred distances are discrepant with the Pantheon+ SnIa distances across all redshift bins considered, with the discrepancy level varying with redshift. 2) The distance discrepancy is more pronounced at lower redshifts ($z \in [0.1,0.8]$) compared to higher redshifts ($z\in [0.8,2.3]$). The consistency of $Λ$CDM best fit parameters obtained in high and low redshift bins of both BAO and SnIa samples is investigated and we confirm that the tension reduces at high redshifts. Also a mild tension between the redshift bins is identified at higher redshifts for both the BAO and Pantheon+ data with respect to the best fit value of $H_0$ in agreement with previous studies which find hints for an 'evolution' of $H_0$ in the context of $Λ$CDM. These results confirm that the low redshift BAO and SnIa distances can only become consistent through a re-evaluation of the distance calibration methods. An $H(z)$ expansion rate deformation alone is insufficient to resolve the tension. Our findings also hint at a possible deviation of the expansion rate from the Planck18/$Λ$CDM model at high redshifts $z\gtrsim 2$. We show that such a deformation is well described by a high redshift transition of $H(z)$ like the one expressed by $Λ_s$CDM even though this alone cannot fully resolve the Hubble tension due to its tension with intermediate/low $z$ BAO data.

Figures (4)

• Figure 1: The binned BAO and Pantheon+ luminosity distance moduli (residuals with respect to the Planck18/$\Lambda$CDM ). The residual distance moduli for the best fit $wCDM$ and $\Lambda_{\rm s}$CDM are also shown. Larger redshift bins are shown in the right panel. The inconsistency between BAO and SnIa measured distance moduli is evident. The full Pantheon+ distance moduli are also shown in the grey background. The green points correspond to the latest DESI BAO data.
• Figure 2: The consistency between BAO and Pantheon+ data for the low (left) and high (right) redshift bins. Notice that the discrepancy is significantly larger for the low redshift bin.
• Figure 3: The consistency between low and high redshift bins for BAO (left) and Pantheon+ (right) data. Notice that there is no evident inconsistency between the redshift bins in the context of each individual dataset.
• Figure 4: The likelihood contours of $\Lambda$CDM parameters obtained with the full BAO and Pantheon+ samples. The tension between the total BAO and Pantheon+ data sets in intermediate redshifts is apparent.