# Alleviating the $H_0$ tension in Rastall gravity

## TL;DR

This paper explores the Rastall $\\Lambda$CDM model as a way to reduce the $H_0$ tension in cosmology, finding it alleviates the discrepancy with local measurements but does not resolve the $\sigma_8$ tension.

## Contribution

It introduces and constrains the Rastall gravity framework within cosmology, demonstrating its potential to mitigate the $H_0$ tension compared to standard models.

## Key findings

- The Rastall $\\Lambda$CDM model reduces the $H_0$ tension to about 2 sigma.
- Closed geometry in the model further alleviates the $H_0$ discrepancy.
- The $\sigma_8$ tension remains unresolved in this framework.

## Abstract

The tension between measurements of the Hubble constant $H_0$ locally and the value inferred from Planck satellite have provided a strong motivation to explore theoretical frameworks beyond the standard cosmological model ($\Lambda$CDM). To this aim, we investigate the $H_0$ tension in the Rastall $\Lambda$CDM model (R-$\Lambda$CDM), formulated within the Rastall gravity framework as a phenomenological extension of General Relativity featuring a non-conserved energy-momentum tensor. To constrain the cosmological parameters, we employ a comprehensive combined dataset including Big Bang Nucleosynthesis (BBN), Hubble parameter $H(z)$, Type Ia supernovae (SNe Ia), Baryon Acoustic Oscillations (BAO), Cosmic Microwave Background (CMB) anisotropies, and the growth rate of cosmic structures $f(z)\sigma_8(z)$. The estimation of model parameters is performed via Markov Chain Monte Carlo (MCMC) sampling within a Bayesian statistical framework. Our results show that the R-$\Lambda$CDM model, especially in closed geometry, reduces the $H_0$ tension, bringing the discrepancy with the local SH0ES measurements down to $1.97\sigma$ to $2.18\sigma$. However, the tension related to the $\sigma_8$ parameter remains unresolved.