Uncalibrated Cosmic Standards as a Robust Test on Late-time Cosmological Models

Abstract We present an assumption-minimized framework for testing late-time cosmological models using uncalibrated cosmic standards (UCS)—including standard rulers and standard candles—without relying on absolute calibrations. The method exploits a tight, model-insensitive correlation between the sound horizons at recombination and the drag epoch. By avoiding dependence on prerecombination physics and the amplitude of the cosmic microwave background (CMB) power spectra, the UCS framework reduces potential early-Universe biases while retaining much of the constraining power of full analyses. Applying UCS to the recent dynamical dark energy study that reported deviations from ΛCDM, we find the constraints shift systematically toward the ΛCDM case. If this shift is physical, it may result from the omission of some prerecombination physical processes that influence the scale dependence of the CMB spectra. We also observe a mild tension between uncalibrated standard rulers and candles, which can be largely mitigated by introducing a redshift-dependent magnitude bias in the Type Ia supernovae data. Our results highlight the importance of isolating postrecombination observables for testing late-time models in the era of precision cosmology, positioning UCS analysis as a robust framework for upcoming galaxy surveys.