What question did this study set out to answer?

This research aims to impose observational constraints on a modified cosmological model, focusing on the expansion rate.

May 1, 2026Open Access

Scalar–Tensor Cosmology with Time-Scaling Modification: Observational Constraints from H(z) and Pantheon+

Key Points

This research aims to impose observational constraints on a modified cosmological model, focusing on the expansion rate.
Used cosmic chronometer H(z) data and Pantheon+ Type Ia supernova sample (N=1701) for analysis.
Conducted a joint chi-squared fit, employing a full covariance matrix.
Analyzed improvements in fit metrics compared to the standard Lambda Cold Dark Matter model (ΛCDM).
Observed Δχ² ≈ -12.67 indicating significant improvement over ΛCDM.
ΔAIC ≈ -10.67 further supports the enhancement of model fit.
Best-fit value C ≈ 0.12 suggests time-dependent expansion rate modifications, stronger at higher redshift.

Abstract

Version 2 update: This version introduces observational constraints on the model using: - Cosmic chronometer H(z) data- Pantheon+ Type Ia supernova sample (N = 1701)- Full covariance matrix A joint χ² fit is performed, showing an improvement over ΛCDM: Δχ² ≈ -12.67 ΔAIC ≈ -10.67 The improvement arises primarily from the supernova sector, while remaining consistent with H(z) constraints. The best-fit value C ≈ 0.12 suggests a time-dependent modification of the expansion rate, stronger at higher redshift. The repository containing the code used in this analysis is available at:https://github.com/Jabukovac/psi-time-cosmology These results are preliminary and future work will include BAO/CMB constraints and full statistical analysis.

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