Isotropization of the universe during inflation

Abstract

A primordial inflationary phase allows one to erase any possible anisotropic expansion thanks to the cosmic no-hair theorem. If there is no global anisotropic stress, then the anisotropic expansion rate tends to decrease. What are the observational consequences of a possible early anisotropic phase? We first review the dynamics of anisotropic universes and report analytic approximations. We then discuss the structure of dynamical equations for perturbations and the statistical properties of observables, as well as the implication of a primordial anisotropy on the quantization of these perturbations during inflation. Finally we briefly review models based on primordial vector field which evade the cosmic no-hair theorem.

9 pages, 3 figures. Invited review article for the French Academy of Science

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• Structure formation in an anisotropic universe: Eulerian perturbation theory
• Thermodynamics of Shearing Massless Scalar Field Spacetimes is Inconsistent With the Weyl Curvature Hypothesis
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• Nonlinear anisotropy growth in Bianchi-I spacetime in metric $f(R)$ cosmology
• Anisotropic chiral cosmology: exact solutions
• Canonical equivalence, quantization and anisotropic inflation in higher order theory of gravity
• Classical and quantum exact solutions for the anisotropic Bianchi type I in multi-scalar field cosmology with an exponential potential driven inflation
• Bianchi cosmologies in a Thurston-based theory of gravity