Malgorzata Bogdan

Professor

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

Författare

Maria Giovanna Dainotti
Biagio De Simone
Tiziano Schiavone
Giovanni Montani
Enrico Rinaldi
Gaetano Lambiase
Malgorzata Bogdan
Sahil Ugale

Summary, in English

The difference from 4 to 6 σ in the Hubble constant (H₀ ) between the values observed with the local (Cepheids and Supernovae Ia, SNe Ia) and the high-z probes (Cosmic Microwave Background 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) = H₀/(1 + z)^η, where H₀ is H₀ (z = 0) and η is the evolutionary parameter. Here, we investigate if this evolution still holds by using the SNe Ia gathered in the Pantheon sample and the Baryon Acoustic Oscillations. We assume H₀ = 70 km s⁻¹ Mpc⁻¹ as the local value and divide the Pantheon into three bins ordered in increasing values of redshift. Similar to our previous analysis but varying two cosmological parameters contemporaneously (H₀, Ω_0m in the ΛCDM model and H₀, w_a in the w₀w_aCDM model), for each bin we implement a Markov-Chain Monte Carlo analysis (MCMC) obtaining the value of H₀ assuming Gaussian priors to restrict the parameters spaces to values we expect from our prior knowledge of the current cosmological models and to avoid phantom Dark Energy models with w < −1. Subsequently, the values of H₀ are fitted with the model f (z). Our results show that a decreasing trend with η ∼ 10⁻² is still visible in this sample. The η coefficient reaches zero in 2.0 σ for the ΛCDM model up to 5.8 σ for w₀w_aCDM 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 analysis is meant to further cast light on the evolution of H₀ and it does not specifically focus on constraining the other parameters. This work is also a preparatory to understand how the combined probes still show an evolution of the H₀ by redshift and what is the current status of simulations on GRB cosmology to obtain the uncertainties on the Ω_0m comparable with the ones achieved through SNe Ia.