Reconstructing the redshift evolution of Type Ia supernovae absolute magnitude

This work investigates a potential time dependence of the absolute magnitude of Type Ia Supernovae (SN Ia). Employing the Gaussian Process approach, we obtain the SN Ia absolute magnitude and its derivative as a function of redshift. The data set considered in the analysis comprises measurements of apparent magnitude from SN Ia, Hubble rate from cosmic chronometers, and the ratio between angular and radial distances from Large-Scale Structure data (BAO and voids). Our findings reveal good compatibility between the reconstructed SN Ia absolute magnitudes and a constant value. However, the mean value obtained from the Gaussian Process reconstruction is $M=-19.456\pm 0.059$, which is $3.2σ$ apart from local measurements by Pantheon+SH0ES. This incompatibility may be directly associated to the $Λ$CDM model and local data, as it does not appear in either model-dependent or model-independent estimates of the absolute magnitude based on early universe data. Furthermore, we assess the implications of a variable $M$ within the context of modified gravity theories. Considering the local estimate of the absolute magnitude, we find $\sim3σ$ tension supporting departures from General Relativity in analyzing scenarios involving modified gravity theories with variations in Planck mass through Newton's constant.