Probing potential redshift-dependent systematics in the Hubble tension: Model-independent $H_0$ constraints from DESI R2

TL;DR

The paper tackles the Hubble tension by introducing a cosmology-model-independent, geometric method to determine $H_0$ using a joint analysis of SN Ia, BAO, and cosmic chronometer data. It leverages Gaussian process regression to reconstruct the expansion history from Pantheon Plus SN Ia and CC $H(z)$ while using DESI DR2 BAO measurements with full covariance, all grounded in the distance duality relation to eliminate dependence on the sound horizon scale. The authors generate 1000 GP realizations, propagate uncertainties through a hierarchical Monte Carlo framework, and derive $H_0$ constraints at five redshifts, finally combining them into a single, robust $H_0$ estimate of $69.29 \pm 0.81$ km s$^{-1}$ Mpc$^{-1}$ (1.2% precision). They find a non-monotonic redshift pattern in $H_0$ that is not statistically significant ($p=0.208$) and thus cannot decisively resolve the tension, but the multi-redshift constraints provide a powerful cross-check against traditional distance ladder measurements and a pathway to test redshift-dependent systematics with future data.

Abstract

We present a determination of the Hubble constant ($H_0$) using the latest observational data from multiple cosmological probes, providing an independent geometric calibration of the SN Ia distance scale. By combining baryon acoustic oscillation (BAO) measurements from the second data release of the Dark Energy Spectroscopic Instrument (DESI DR2), cosmic chronometer $H(z)$ data, and the Pantheon Plus Type Ia supernova (SN Ia) sample, we reconstruct the cosmic expansion history through Gaussian process regression without assuming a specific cosmological model. Our analysis fully incorporates the complete covariance structure and yields $H_0$ constraints at five distinct redshifts: $65.72 \pm 1.99$ (z=0.51), $67.78 \pm 1.75$ (z=0.706), $70.74 \pm 1.39$ (z=0.934), $71.04 \pm 1.93$ (z=1.321), and $68.37 \pm 3.95~\mathrm{km~s^{-1}~Mpc^{-1}}$ (z=1.484). The Bayesian combination of these measurements gives $\hat{H}_0 = 69.29 \pm 0.81~\mathrm{km~s^{-1}~Mpc^{-1}}$ with 1.2\% precision, which occupies an intermediate position between the Planck CMB result and the SH0ES local measurement. While we observe a non-monotonic pattern in $H_0$ values across redshifts, statistical tests show this apparent evolution is not significant (p = 0.208). Our approach delivers independent constraints at multiple redshifts, enabling investigation of potential redshift-dependent systematic effects in the Hubble tension. The results demonstrate that an independent geometric method yields an $H_0$ value consistent with the intermediate range of current measurements, providing a crucial cross-check of distance ladder determinations.

Figures (4)

• Figure 1: The reconstructed apparent magnitude $m_B$ using GPR from the Pantheon Plus dataset for a representative sample of the 1000 GP realizations.
• Figure 2: The reconstructed Hubble parameter $[H(z)]^{\rm CC}$ using GPR from the 32 CC dataset for a representative sample of the 1000 GP realizations.
• Figure 3: The marginalized distributions of Hubble constant measurements at five distinct redshifts. The diagonal panels show the one-dimensional posterior distributions of $H_0$ at each redshift, with mean values and standard deviations indicated. The lower off-diagonal panels display the two-dimensional joint distributions between different redshift measurements, with correlation coefficients $\rho$ annotated. The measurements show significant correlations between adjacent redshift bins. The color scale represents the density of samples in the parameter space. These correlations arise from the covariance structure of BAO measurements and the smoothing effects introduced by Gaussian process reconstruction. The bottom labels indicate the corresponding redshift for each column and row.
• Figure 4: The marginal $H_0$ measurements at five redshifts are shown with error bars. The combined result $\hat{H}_0=69.0\pm 1.0$ km/s/Mpc (green band) is compared with Planck (red) and SH0ES (blue) measurements. The data show a non-monotonic trend with redshift.