Constraining the anisotropy of the Universe via Pantheon supernovae sample

TL;DR

This study investigates the potential dipole anisotropy in the universe using Pantheon supernova data across various cosmological models, finding very weak anisotropy likely due to sample inhomogeneity.

Contribution

It applies Finslerian and dipole-modulated cosmological models to Pantheon data and assesses anisotropy, highlighting the importance of sample homogeneity for accurate constraints.

Findings

Dipole anisotropy is very weak in all models.

Dipole directions align with the SDSS subsample plane.

Inhomogeneous data distribution may bias anisotropy detection.

Abstract

We test the possible dipole anisotropy of a Finslerian cosmological model and other three dipole-modulated cosmological models, i.e., the dipole-modulated $\rm{\Lambda}$CDM, $w$CDM and Chevallier--Polarski--Linder (CPL) model by using the recently released Pantheon sample of SNe Ia. The Markov chain Monte Carlo (MCMC) method is used to explore the whole parameter space. We find that the dipole anisotropy is very weak in all cosmological models used. Although the dipole amplitudes of four cosmological models are consistent with zero within $1\sigma$ uncertainty, the dipole directions are close to the axial direction to the plane of SDSS subsample among Pantheon. It may imply that the weak dipole anisotropy in the Pantheon sample originates from the inhomogeneous distribution of the SDSS subsample. More homogeneous distribution of SNe Ia is necessary to constrain the cosmic anisotropy.