Constraints on an Anisotropic Universe

Abstract

We analyze the possibility of global anisotropy of the universe. We consider an altered Friedmann Lemaitre Robertson Walker metric in which there are different scale factors along the three different axes of space. We construct the corresponding altered Friedmann equations. We show that any initial anisotropies decrease into the future. At late times, the difference in Hubble parameters changes as $1/\sqrt{t}$ in a radiation dominated era and as $1/t$ in a matter dominated era. We use constraints from Big Bang Nucleosynthesis and the Cosmic Microwave Background to constrain the level of anisotropies at early times. We also examine how the approach back in time to the singularity is radically altered; happening much more abruptly, as a function of density, in an anisotropic universe. We also mention improved bounds that can arise from measurements of primordial gravitons, Weakly interacting massive particles, and neutrinos.

arXiv comment10 pages in double column format, 4 figures. V2: Added references. V3: Updated towards version published in Phys. Rev. D

References in corpus (10)

• Is the Observable Universe Consistent with the Cosmological Principle?
• Ellipsoidal Universe Can Solve The CMB Quadrupole Problem
• Constraints on a Bianchi type I spacetime extension of the standard $\Lambda$CDM model
• Revisiting Cosmic No-Hair Theorem for Inflationary Settings
• The challenge of ruling out inflation via the primordial graviton background
• Testing spatial curvature and anisotropic expansion on top of the $\Lambda$CDM model
• Current Constraints on Anisotropic and Isotropic Dark Energy Models
• Bianchi I meets the Hubble diagram
• Measuring Hubble constant in an anisotropic extension of $\Lambda$CDM model
• Thermal leptogenesis in anisotropic cosmology

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• DESIgning concordant distances in the age of precision cosmology: the impact of density fluctuations
• Anisotropic Generalization of the ΛCDM Universe Model with Application to the Hubble Tension
• Ellipsoidal Universe and Cosmic Shear
• Constraining Axially Symmetric Bianchi Type I Model with Self-Consistent Recombination History and Observables
• Inferred Hubble Parameter from Gravitational Waves in a Perturbative Bianchi I Background
• A Quantitative Framework for Testing the Hubble Tension in a Bianchi Type I Cosmological Background
• Evolution of superhorizon perturbations in early Universe with anisotropic solid remnant