On the evolution of the Hubble constant with the SNe Ia Pantheon Sample and Baryon Acoustic Oscillations: a feasibility study for GRB-cosmology in 2030

TL;DR

This study investigates the evolution of the Hubble constant using the Pantheon SNe Ia sample and BAO data, exploring whether a redshift-dependent evolution persists and its implications for cosmology and gravity theories.

Contribution

It provides a comprehensive analysis of Hubble constant evolution with redshift using combined SNe Ia and BAO data, considering multiple cosmological models and potential astrophysical biases.

Findings

A decreasing trend in H_0 with redshift is observed, with eta around 10^{-2}.

The evolution parameter eta is consistent with zero within 2 sigma for Lambda CDM.

The trend could be due to astrophysical biases or indicate new physics such as modified gravity.

Abstract

The difference from 4 to 6 $\sigma$ in the Hubble constant ($H_0$) between the values observed with the local (Cepheids and Supernovae Ia, SNe Ia) and the high-z probes (CMB obtained by the Planck data) still challenges the astrophysics and cosmology community. Previous analysis has shown that there is an evolution in the Hubble constant that scales as $f(z)=\mathcal{H}_{0}/(1+z)^{\eta}$, where $\mathcal{H}_0$ is $H_{0}(z=0)$ and $\eta$ is the evolutionary parameter. Here, we investigate if this evolution still holds by using the SNe Ia gathered in the Pantheon sample and the BAOs. We assume $H_{0}=70 \textrm{km s}^{-1}\textrm{Mpc}^{-1}$ as the local value and divide the Pantheon into 3 bins ordered in increasing values of redshift. Similar to our previous analysis but varying two cosmological parameters contemporaneously ($H_0$, $\Omega_{0m}$ in the $\Lambda$CDM model and $H_0$, $w_a$ in the $w_{0}w_{a}$CDM model), for each bin we implement a MCMC analysis obtaining the value of $H_0$ $[...]$. Subsequently, the values of $H_0$ are fitted with the model $f(z)$. Our results show that a decreasing trend with $\eta \sim10^{-2}$ is still visible in this sample. The $\eta$ coefficient reaches zero in 2.0 $\sigma$ for the $\Lambda$CDM model up to 5.8 $\sigma$ for $w_{0}w_{a}$CDM model. This trend, if not due to statistical fluctuations, could be explained through a hidden astrophysical bias, such as the effect of stretch evolution, or it requires new theoretical models, a possible proposition is the modified gravity theories, $f(R)$ $[...]$. This work is also a preparatory to understand how the combined probes still show an evolution of the $H_0$ by redshift and what is the current status of simulations on GRB cosmology to obtain the uncertainties on the $\Omega_{0m}$ comparable with the ones achieved through SNe Ia.