{"about":{"site":"https://codewithpapers.app","non_affiliation":"Code with Papers and Syntology are not affiliated with, endorsed by, or sponsored by Papers with Code, Meta, or the pwc-archive mirror.","licence":"CC BY-SA 4.0","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","attribution":"https://codewithpapers.app/attribution","modified":"archive material modified by Syntology; see the attribution page"},"url":"/paper/on-the-homogeneity-of-snia-absolute-magnitude","title":"On the homogeneity of SnIa absolute magnitude in the Pantheon+ sample","arxiv_id":"2301.01024","date":"2023-01-03","proceeding":null,"authors":["Leandros Perivolaropoulos","Foteini Skara"],"abstract":"We have analysed the Pantheon+ sample using a new likelihood model that replaces the single SnIa absolute magnitude parameter $M$ used in the standard likelihood model of Brout et. al. with two absolute magnitude parameters $M_<$, $M_>$ and a transition distance $d_{crit}$ that determines the distance at which $M$ changes from $M_<$ to $M_>$. The use of this likelihood dramatically changes the quality of fit to the Pantheon+ sample for a $\\Lambda$CDM background by $\\Delta \\chi^2=-19.6$. The tension between the $M_<$ and $M_>$ best fit values is at a level more than $3\\sigma$ with a best fit $d_{crit}$ very close to $20Mpc$. The origin of this improvement of fit and $M_<-M_>$ tension is that the new likelihood model, successfully models two signals hidden in the data: 1. The well known systematic effect called 'volumetric redshift scatter bias' which is due to asymmetric peculiar velocity variations at redshifts $z<0.01$ induced by unequal projected volumes at lower and higher distances compared to a given distance and 2. A mild signal for a change of intrinsic SnIa luminosity at about $20Mpc$. This interpretation of the results is confirmed by truncating the $z<0.01$ Hubble diagram data from Pantheon+ where the above systematic is dominant and showing that the $M_<-M_>$ tension decreases from above $3\\sigma$ to a little less than $2\\sigma$. It is also confirmed by a Monte Carlo simulation comparing the SnIa absolute luminosities $M_i$ of SnIa+Cepheid hosts, with the anticipated luminosities in the context of a homogeneous single absolute magnitude $M$. This simulation shows that the maximum significance of the SnIa luminosity transition ($\\Sigma\\equiv \\frac{|M_>-M_<|}{\\sqrt{\\sigma_{M_>}^2+\\sigma_{M_<}^2}}$) in the real data, is larger than the corresponding maximum significance of $94\\%$ of the corresponding homogeneous simulated samples.","url_abs":"https://arxiv.org/abs/2301.01024v2","url_pdf":"https://arxiv.org/pdf/2301.01024v2.pdf","source":{"archive":"pwc-archive (Hugging Face), CC BY-SA 4.0","snapshot":"2025-07-28","licence_url":"https://creativecommons.org/licenses/by-sa/4.0/legalcode","row_kind":"links_only","authors_date_abstract":"arXiv metadata, CC0 1.0 (https://info.arxiv.org/help/license), from the Kaggle arXiv metadata snapshot of 2026-09-12"},"code_links":[{"paper_slug":"on-the-homogeneity-of-snia-absolute-magnitude","repo_url":"https://github.com/leandros11/pantheonplus1","is_official":1,"mentioned_in_paper":1,"mentioned_in_github":0,"framework":"none","reach":null}],"tasks":[],"methods":[],"datasets_introduced":[],"methods_introduced":[],"results":[],"syntology":{"syntology_url":null,"atlas_url":null,"mcp":null,"developers":"https://syntology.ai/developers"},"arxiv_metadata":null,"syntology_extracted_results":null}