Papers › Hubble tension or a transition of the Cepheid SnIa calibrator parameters?
Hubble tension or a transition of the Cepheid SnIa calibrator parameters?
Leandros Perivolaropoulos, Foteini Skara
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We re-analyze the Cepheid data used to infer the value of H₀ by calibrating SnIa. We do not enforce a universal value of the empirical Cepheid calibration parameters R_W (Cepheid Wesenheit color-luminosity parameter) and M_Hᵂ (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 3σ level mismatch between the low and high galactic distance parameter values. We then use AIC and BIC criteria to compare and rank the following types of models: Base models: Universal values for R_W and M_Hᵂ (no parameter variation), I Individual fitted galactic R_W with a universal fitted M_Hᵂ, II Universal fixed R_W with individual fitted galactic M_Hᵂ, III Universal fitted R_W with individual fitted galactic M_Hᵂ, IV Two universal fitted R_W (near and far) with one universal fitted M_Hᵂ, V Universal fitted R_W with two universal fitted M_Hᵂ (near and far), VI Two universal fitted R_W with two universal fitted M_Hᵂ (near and far). We find that the AIC and BIC 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 H₀ implied by the favored model IV is consistent with the inverse distance ladder calibration based on the CMB sound horizon H₀=67.4±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.
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