Redshift-binned constraints on the Hubble constant under $Λ$CDM, CPL, and Padé cosmography

Motivated by recent claims of a possible redshift dependence in late-Universe determinations of the Hubble constant (H_0), we test the robustness of this behavior using multiple cosmological probes. We perform a joint redshift-binned analysis of H_0 across eight bins using late-Universe probes including Pantheon+ type Ia supernovae, Dark Energy Spectroscopic Instrument baryon acoustic oscillations, cosmic chronometers, and water megamasers under three cosmological frameworks: flat Lambda cold dark matter, Chevallier-Polarski-Linder, and Pade cosmography. Under a common baseline scheme, all three models show a qualitatively similar low-amplitude variation in the per-bin H_0 estimates. A simple Fourier-like parametrization captures this behavior, but the amplitude differs from zero only at a marginal significance of about 1.71-1.94 sigma, with similar behavior observed across all three cosmological frameworks. We then investigate the robustness and possible origin of this feature. Alternative binning schemes preserve its qualitative form, whereas single-probe per-bin fits (supernova-only, cosmic chronometer-only, BAO-only) yield ratios H_0,i / H_0,global mostly consistent with unity and do not reproduce the pronounced drift seen in the joint baseline constraints. Finally, by comparing different global versus piecewise-constant configurations for {H_0, Omega_m, M, r_d}, we find that a baselinelike oscillatory pattern reemerges only when multiple degenerate parameter combinations are allowed to vary across bins, while it is strongly suppressed when only H_0 is bin dependent. Taken together, these results indicate that the apparent oscillatory behavior of H_0(z) in late time arises from known parameter degeneracies and does not constitute robust evidence for a genuine redshift evolution.

💡 Research Summary

The paper addresses the ongoing debate about a possible redshift dependence of the Hubble constant (H₀) in late‑Universe measurements, a topic that has gained attention as a potential contributor to the well‑known H₀ tension. The authors assemble a comprehensive late‑time data set consisting of Pantheon+ Type Ia supernovae (SNe Ia), DESI baryon acoustic oscillation (BAO) measurements, cosmic chronometers (CC), and water megamaser distances. They divide the combined data into eight redshift bins (the primary “A0” scheme) chosen so that each bin contains sufficient constraining power and the effective redshifts of the different probes within a bin are consistent.

Three cosmological frameworks are employed: (i) flat ΛCDM (parameters H₀, Ωₘ), (ii) the Chevallier‑Polarski‑Linder (CPL) dark‑energy parametrization (adding w₀, wₐ), and (iii) Padé 2‑1 cosmography (parameters H₀, deceleration q₀, jerk j₀). For each bin and each model the authors run Bayesian Markov‑Chain Monte Carlo (MCMC) analyses using the EMCEE sampler, with uniform priors on all free parameters and Gaussian likelihoods constructed from the published data covariances.

The baseline results show that all three models produce per‑bin H₀ estimates that fluctuate around a common mean with a low‑amplitude, roughly sinusoidal pattern. Fitting a simple Fourier‑like function H₀(z)=H̄₀