The nonlinear patterns of the cosmic anisotropy: the spatially flat perfect fluid universes

Abstract

Abstract In this manuscript, we investigate the patterns of the cosmological anisotropy in the spatially flat Bianchi models filled with a perfect fluid. We analyse the factor 1 + Δ R , the ratio of the Hubble parameter in the anisotropic model over its isotropic counterpart. In general, Δ R starts to deviate significantly from zero at a specific redshift z A , which depends on the type of the fluid and the value of the anisotropy magnitude. We also show that the deceleration and the jerk along the principal directions of the expansion tensor are constrained by simple algebraic equations that do not depend on the type of matter present. These characteristic patterns form a valuable framework to probe the cosmological anisotropy in the late-time universe.