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

TL;DR

This paper introduces a calibration-independent framework using Uncalibrated Cosmic Standards to test late-time cosmological models, reducing early-Universe biases and providing robust constraints for future galaxy surveys.

Contribution

It develops a model-insensitive method leveraging a correlation between sound horizons, avoiding reliance on pre-recombination physics, and applies it to dynamical dark energy studies.

Findings

Constraints shift towards ΛCDM when using UCS

Mild tension observed between standard rulers and candles

Redshift-dependent bias can mitigate data tensions

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 pre-recombination 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 (DE) study that reported deviations from $\Lambda$CDM, we find the constraints shift systematically toward the $\Lambda$CDM case. If this shift is physical, it may result from the omission of some pre-recombination 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 supernova (SNe Ia) data. Our results highlight the importance of isolating post-recombination observables for testing late-time models in the era of precision cosmology, positioning UCS analysis as a robust framework for upcoming galaxy surveys.