2019/05/31 by Özgür Akarsu, Ozgur Akarsu, Suresh Kumar +2 · 120 citations
Physics and Astronomy · #Anisotropy #Astrophysics #Black Holes and Theoretical Physics #Combinatorics #Cosmic microwave background #Cosmology and Gravitation Theories #Dimension (graph theory) #Mathematical physics #Omega #Particle physics #Particle physics theoretical and experimental studies #Physics #Quantum mechanics #Redshift #Standard Model (mathematical formulation) #Type (biology) #Universe #astro-ph.CO #gr-qc
paper · pdf · doi:10.1103/physrevd.100.023532
published in Physical review. D/Physical review. D. 100(2) (American Physical Society) · 13 pages, 4 figures, 5 tables; Matches the published version in Physical Review D
openalex created_date 2019/05/29 · openalex publication_date 2019/07/23 · arxiv created 2019/07/24 · arxiv updated 2019/07/25 · openalex updated_date 2026/08/05
We consider the simplest anisotropic generalization, as a correction, to the standard \mathrm\ensuremathΛCDM model, by replacing the spatially flat Robertson-Walker metric by the Bianchi type-I metric, which brings in a new term \mathrm\ensuremathΩ_\ensuremathσ0a^\ensuremath-6 (mimicking the stiff fluid) in the average expansion rate H(a) of the Universe. From Hubble and Pantheon data, relevant to the late Universe (z\ensuremath\lesssim2.4), we obtain the constraint \mathrm\ensuremathΩ_\ensuremathσ0\ensuremath\lesssim10^\ensuremath-3, in line with the model-independent constraints. When the baryonic acoustic oscillations and cosmic microwave background (CMB) data are included, the constraint improves by 12 orders of magnitude, i.e., \mathrm\ensuremathΩ_\ensuremathσ0\ensuremath\lesssim10^\ensuremath-15. We find that this constraint could alter neither the matter-radiation equality redshift nor the peak of the matter perturbations. Demanding that the expansion anisotropy has no significant effect on the standard big bang nucleosynthesis (BBN), we find the constraint \mathrm\ensuremathΩ_\ensuremathσ0\ensuremath\lesssim10^\ensuremath-23. We show explicitly that the constraint from BBN renders the expansion anisotropy irrelevant to make a significant change in the CMB quadrupole temperature, whereas the constraint from the cosmological data in our model provides the temperature change up to \text\ensuremath∼11 mK, though it is much beyond the CMB quadrupole temperature.