Hubble tension or a transition of the Cepheid SnIa calibrator parameters?

This repository contains the Mathematica files of arXiv:2109.04406

Abstract

We re-analyze the Cepheid data used to infer the value of the Hubble parameter $H_0$ by calibrating Type Ia supernovae. We do not enforce a universal value of the empirical Cepheid calibration parameters $R_W$ (Cepheid Wesenheit color-luminosity parameter) and $M_H^{W}$ (Cepheid Wesenheit H-band absolute magnitude). Instead we allow for variation of either of these parameters for each individual galaxy. We also consider the case where these parameters have two universal values: one for low galactic distances $D<D_c$ and one for high galactic distances $D>D_c$ where $D_c$ is a critical transition distance. We find hints for a $3\sigma$ level mismatch between the low and high galactic distance parameter values. We then use model selection criteria (AIC and BIC) which penalize models with large numbers of parameters, to compare and rank the following types of $R_W$ and $M_H^W$ parameter variations: Base models: Universal values for $R_W$ and $M_H^W$ (no parameter variation), I: Individual fitted galactic $R_W$ with one universal fitted $M_H^W$, II: One universal fixed $R_W$ with individual fitted galactic $M_H^W$, III: One universal fitted $R_W$ with individual fitted galactic $M_H^W$, IV: Two universal fitted $R_W$ (near and far) with one universal fitted $M_H^W$, V: One universal fitted $R_W$ with two universal fitted $M_H^W$ (near and far), VI: Two universal fitted $R_W$ (near and far) with two universal fitted $M_H^W$ (near and far). We find that the AIC and BIC model selection criteria consistently favor model IV instead of the commonly used Base model where no variation is allowed for the Cepheid empirical parameters. The best fit value of the SnIa absolute magnitude $M_B$ and of $H_0$ implied by the favored model IV is consistent with the inverse distance ladder calibration based on the CMB sound horizon $H_0=67.4\pm 0.5,km,s^{-1},Mpc^{-1}$. Thus in the context of the favored model IV the Hubble crisis is not present. This model may imply the presence of a fundamental physics transition taking place at a time more recent than $100,Myrs$ ago.

Citing the paper

If you use any of the above codes or the figures in a published work please cite the following paper:

Hubble tension or a transition of the Cepheid SnIa calibrator parameters?

Leandros Perivolaropoulos and Foteini Skara arXiv:2109.04406

Any further questions/comments are welcome.

Authors List

Leandros Perivolaropoulos - leandros@uoi.gr

Foteini Skara - f.skara@uoi.gr