Investigating the Hubble Tension and $\sigma_8$ Discrepancy in f(Q) Cosmology

TL;DR

This study explores how a three-parameter $f(Q)$ modified gravity model affects the Hubble tension and $\sigma_8$ discrepancy, finding limited success in resolving these issues with current cosmological probes.

Contribution

It introduces a three-parameter $f(Q)$ model into cosmological analysis and assesses its impact on the Hubble tension and $\sigma_8$ discrepancy using multiple observational probes.

Findings

The model reduces the Hubble tension to 3σ at best.

$\sigma_8$ discrepancy is mitigated on weak lensing scales but reappears with 3×2pt data.

Parameter $eta$ significantly influences the reduction of the $\sigma_8$ discrepancy.

Abstract

In this study, we incorporated a three-parameter family, of the metric incompatible modification of standard general relativity $f(Q)$ models into the Boltzmann code MGCLASS at both the background and perturbation levels, in order to conduct a Bayesian study employing probes that include the cosmic microwave background (CMB), baryon acoustic oscillations (BAO), weak lensing (WL), alone or its correlation with galaxy clustering (3$\times$2pt) and growth measurements $f \sigma_8$, for each submodel. Our analysis focused on the impact of the Hubble tension in $H_0$ and the discrepancy in $\sigma_8$ resulting from the inclusion of our model parameters, namely $M$, $\alpha$ and $\beta$. We find that none of the sub models, considered alone or combined, were able of alleviating the Hubble tension with only reducing it to 3 $\sigma$ in the least constraining, highest degree of freedom case while we found that the $\sigma_8$ discrepancy, already strongly mitigated on WL linear scales, especially when we let all our model's parameters as free, appears again when considering the more constraining 3$\times$2pt probe. Among the parameters considered, we found that $\beta$, acting in scaling both the gravitational and the Hubble parameter, had the most impact in reducing the discrepancy, with data preferring far from $\Lambda$CDM alike values, before the combination with $f \sigma_8$ constrain it back to its general relativity values.