Redshift-binned constraints on the Hubble constant under $\Lambda$CDM, CPL, and Pad\'e cosmography

TL;DR

This study investigates potential redshift dependence of the Hubble constant using multiple cosmological probes and models, finding that observed variations are likely due to parameter degeneracies rather than true evolution.

Contribution

It provides a comprehensive analysis across different models and data sets, demonstrating that apparent H_0(z) oscillations are not robust evidence for evolution but arise from degeneracies.

Findings

Low-amplitude H_0 variation across redshift bins.

Oscillatory patterns linked to parameter degeneracies.

Single-probe fits do not reproduce the drift.

Abstract

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.