What question did this study set out to answer?

The aim is to present a minimal extension to the ΛCDM model that addresses tensions in late-time cosmic expansion data.

April 14, 20260 citationsOpen Access

R-Universe: A Minimal Extension of ΛCDM Preferred by Late-Time Expansion Data

MPMartin PetrásekInstitute of Organic Synthesis

Key Points

The aim is to present a minimal extension to the ΛCDM model that addresses tensions in late-time cosmic expansion data.
Introduced the R-Universe model with one additional parameter for dark energy evolution.
Conducted a joint analysis using Type Ia supernovae (Pantheon+), cosmic chronometers, and baryon acoustic oscillations.
Performed statistical model comparisons using χ² fitting and Bayesian Information Criterion (BIC).
Achieved a statistically significant improvement over the ΛCDM model with Δχ² ≈ 37 and ΔBIC ≈ −30.
Provided strong evidence for a modified expansion history of the universe.

Abstract

This work presents a minimal extension of the standard cosmological model (ΛCDM), referred to as the R-Universe, motivated by tensions among independent probes of late-time cosmic expansion. The model introduces a single additional parameter modifying the effective evolution of dark energy. Using a joint analysis of Type Ia supernovae (Pantheon+), cosmic chronometers, and baryon acoustic oscillations, we find a statistically significant improvement over ΛCDM: - Δχ² ≈ 37 - ΔBIC ≈ −30 These results indicate strong evidence in favor of a modified expansion history, suggesting that late-time cosmological data may not be fully consistent with a strictly constant vacuum energy component. The repository includes:- Full analysis code for ΛCDM and R-Universe models - Implementation of χ² fitting and BIC comparison - Tools for reproducing all main results The code is designed for full reproducibility of the results presented in the associated manuscript.

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