Bianchi Type I Model Cannot Explain the Observed CMB Angular Acoustic Scale Directional Variation

Abstract

Anisotropic cosmological models have been gaining attention due to various observational hints of large-scale anisotropies. One of the most surprising evidences for the latter is the discovery of a dipole-like directional variation in cosmological parameters extracted from the Cosmic Microwave Background (CMB) data. In this work, we show that the directional variation of the CMB angular acoustic angle calculated with the fully asymmetric Bianchi Type I metric, a simple extension of the standard Friedmann-Lema\^itre-Robertson-Walker metric, cannot account for the observed dipole-like anisotropy.