Letter to the Editor

Redshift dependence of type Ia supernova standardization parameters and implications for cosmological inference

¹ Byurakan Astrophysical Observatory (BAO) after V. Ambartsumian, NAS of the Republic of Armenia Byurakan, Aragatzotn Province, 0213, Republic of Armenia
² Institute of Applied Problems of Physics, NAS of the Republic of Armenia 25 Hrachya Nersissian Str., Yerevan, 0014, Republic of Armenia
³ George Brown College, 175 Kendal Ave, Toronto, ON, M5R 3S8, Canada

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 17 March 2026
Accepted: 5 May 2026

Abstract

Context. Type Ia supernovae (SNe Ia) are fundamental probes of cosmic expansion, whose luminosities are empirically standardized using correlations with light-curve stretch and color. A common assumption in cosmological analyses is that the standardization coefficients are independent of redshift.

Aims. We test the internal consistency of this assumption by searching for a possible redshift dependence in the effective empirical calibration of SNe Ia.

Methods. We analyzed a compilation of type Ia supernovae, Pantheon+. We allowed the stretch and color coefficients of the SALT2 framework to vary linearly with redshift and performed a full covariance likelihood analysis using Markov chain Monte Carlo sampling. The model comparison was carried out using χ² statistics and information criteria.

Results. The redshift-dependent model yields a statistically significant improvement in the goodness of fit relative to the constant-coefficient scenario. Allowing for redshift dependence introduces a non-negligible degeneracy between empirical calibration parameters and the inferred matter density parameter Ω_m.

Conclusions. Our results highlight the sensitivity of precision supernova cosmology to assumptions about redshift-independent standardization. The detected trends should be interpreted phenomenologically and may reflect astrophysical evolution, selection effects, or residual systematics. Future analyses combining forward simulations and independent cosmological probes will be essential to clarify their origin and implications.