Hubble tension in an anisotropic Universe

TL;DR

This study investigates whether anisotropic cosmological models can resolve the Hubble tension, using Bayesian methods to constrain model parameters and assess the impact of prior assumptions on the results.

Contribution

It applies a Bayesian inference framework with multiple samplers and priors to test anisotropic models against cosmological data, highlighting the importance of prior choices.

Findings

Anisotropic models remain viable in cosmology.

Data suggests possible anisotropies in the Universe.

No resolution of Hubble tension found with current model.

Abstract

We explore the Hubble tension within an anisotropic cosmological framework by revisiting the Bianchi type-I model introduced in Le Delliou et al. 2020. Motivated by ongoing debates surrounding back-reaction effects and observed anomalies in the cosmic microwave background (CMB), we investigate whether a departure from isotropy in the late Universe could reconcile the observed discrepancies in Hubble constant measurements. Using a Bayesian inference framework, we constrain the model parameters employing multiple nested sampling algorithms: bilby, PyMultiNest, and nessai. We perform the analysis under both uniform and Gaussian priors, allowing us to systematically assess the sensitivity of the inferred cosmological parameters to different prior assumptions. This dual-prior strategy balances agnostic parameter exploration with constraints informed by theory and observation. Our findings demonstrate the reliability of our inference pipeline across different samplers and emphasize the crucial role of prior selection in non-standard cosmological model testing. The results suggest that anisotropic models remain viable contenders in addressing current cosmological tensions: even though the present model does not show alleviation of the Hubble tension, the data points towards anisotropies. Future work may extend this methodology to more complex anisotropic scenarios and incorporate additional cosmological probes such as CMB polarization and gravitational wave standard sirens.