A null test of the Cosmological Principle with BAO measurements

TL;DR

This study tests the fundamental FLRW assumption of cosmology using BAO measurements and Gaussian Processes, finding a mild deviation at low redshift under certain priors but generally confirming FLRW at higher redshifts.

Contribution

It introduces a model-independent null test of the FLRW metric using BAO data and explores the effects of different priors and reconstruction methods.

Findings

Mild deviation from FLRW at low redshift with SH0ES prior

No significant deviation with Planck prior

Reconstruction kernels influence statistical significance

Abstract

The assumption of a Friedmann-Lema\^itre-Roberton-Walker (FLRW) Universe is one of the fundamental pillars of modern Cosmology. It is crucial to confront it against cosmological observations in order to confirm (or rule out) the validity of the $\Lambda$CDM paradigm. We perform a consistency test of the FLRW metric using measurements of both radial and transversal modes of Baryonic Acoustic Oscillations in a model-independent fashion using Gaussian Processes. The impact of different prior assumptions for the sound horizon scale and the Hubble Constant is also explored. We find a mild deviation of the FLRW hypothesis ($\gtrsim 3\sigma$ confidence level) at lower redshift ranges ($0.1<z<0.3$) under the assumption the SH0ES $H_0$ prior, which does not occur for the $H_0$ prior by Planck. We also find that different reconstruction kernels reduce the statistical significance of such a deviation. At higher reshift ranges, the null test are able to confirm the FLRW assumption within $3\sigma$ confidence level regardless of the priors.