On the Hubble Constant Tension in the SNe Ia Pantheon Sample

Abstract

Abstract The Hubble constant (H 0) tension between Type Ia supernovae (SNe Ia) and Planck measurements ranges from 4 to 6σ. To investigate this tension, we estimate H 0 in the ΛCDM and w 0 w a CDM (cold dark matter) models by dividing the Pantheon sample, the largest compilation of SNe Ia, into 3, 4, 20, and 40 bins. We fit the extracted H 0 values with a function mimicking the redshift evolution: g ( z ) = H 0 ( z ) = H ˜ 0 / ( 1 + z ) α , where α indicates an evolutionary parameter and H ˜ 0 = H 0 at z = 0. We set the absolute magnitude of SNe Ia so that H 0 = 73.5 km s − 1 Mpc − 1 , and we fix fiducial values for Ω 0 m Λ CDM = 0.298 and Ω 0 m w 0 w a CDM = 0.308 . We find that H 0 evolves with redshift, showing a slowly decreasing trend, with α coefficients consistent with zero only from 1.2 to 2.0σ. Although the α coefficients are compatible with zero in 3σ, this however may affect cosmological results. We measure locally a variation of H 0 ( z = 0 ) − H 0 ( z = 1 ) = 0.4 km s − 1 Mpc − 1 in three and four bins. Extrapolating H 0 ( z ) to z = 1100, the redshift of the last scattering surface, we obtain values of H 0 compatible in 1σ with Planck measurements independent of the cosmological models and number of bins we investigated. Thus, we have reduced the H 0 tension in the range from 54% to 72% for both cosmological models. If the decreasing trend of H 0 ( z ) is real, it could be due to astrophysical selection effects or to modified gravity.