Impact of the SNe Ia Magnitude Transition at 20 Mpc on Cosmological Parameter Estimation
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| Format: | Preprint |
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2026
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| author | Perivolaropoulos, Leandros Stamou, Chrisostomos-Panagiotis |
| author_facet | Perivolaropoulos, Leandros Stamou, Chrisostomos-Panagiotis |
| contents | We investigate the impact of a late-time transition in the standardized absolute magnitude $M$ on the best-fit values of cosmological parameters using the Pantheon+ dataset. Extending previous analyses which focused on flat $Λ$CDM, we examine this transition within flat $Λ$CDM, wCDM, and CPL cosmologies, as well as a model-independent cosmographic expansion, employing both frequentist ($χ^2$ minimization with \textit{AIC}/\textit{BIC}) and Bayesian (MCMC and Nested Sampling) inference frameworks. We confirm that the data consistently favor a step in absolute magnitude of $ΔM \simeq 0.19~\mathrm{mag}$ at a characteristic distance of $d_{\mathrm{crit}} \approx 20~\mathrm{Mpc}$. The inclusion of this transition leads to a statistically significant improvement in the quality of fit and has a distinct impact on parameter estimation: it induces a systematic increase in the inferred Hubble constant of approximately $2\%$ across all tested models. In contrast, we find that the dynamical parameters governing the background expansion, including the matter density $Ω_m$ and the dark energy equation of state ($w_0, w_a$), remain stable and largely unaffected. These results indicate that the $20~\mathrm{Mpc}$ feature acts primarily as a low-redshift calibration shift rather than a modification of the late-time expansion history. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_12587 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Impact of the SNe Ia Magnitude Transition at 20 Mpc on Cosmological Parameter Estimation Perivolaropoulos, Leandros Stamou, Chrisostomos-Panagiotis Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology We investigate the impact of a late-time transition in the standardized absolute magnitude $M$ on the best-fit values of cosmological parameters using the Pantheon+ dataset. Extending previous analyses which focused on flat $Λ$CDM, we examine this transition within flat $Λ$CDM, wCDM, and CPL cosmologies, as well as a model-independent cosmographic expansion, employing both frequentist ($χ^2$ minimization with \textit{AIC}/\textit{BIC}) and Bayesian (MCMC and Nested Sampling) inference frameworks. We confirm that the data consistently favor a step in absolute magnitude of $ΔM \simeq 0.19~\mathrm{mag}$ at a characteristic distance of $d_{\mathrm{crit}} \approx 20~\mathrm{Mpc}$. The inclusion of this transition leads to a statistically significant improvement in the quality of fit and has a distinct impact on parameter estimation: it induces a systematic increase in the inferred Hubble constant of approximately $2\%$ across all tested models. In contrast, we find that the dynamical parameters governing the background expansion, including the matter density $Ω_m$ and the dark energy equation of state ($w_0, w_a$), remain stable and largely unaffected. These results indicate that the $20~\mathrm{Mpc}$ feature acts primarily as a low-redshift calibration shift rather than a modification of the late-time expansion history. |
| title | Impact of the SNe Ia Magnitude Transition at 20 Mpc on Cosmological Parameter Estimation |
| topic | Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2604.12587 |