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.PACS numbers: 98.80.-k, 98.80.Cq

Anisotropic non-gaussianity from rotational symmetry breaking excited initial states

“…Of the Minkowski isometries, one could also consider constraining the breaking of the boost rota-tion symmetry, or of the translational invariance. In the toy model [2] a particular such generalisation was realised by an x-dependent modulation of the initial condition, but a more proper analysis would require the development of a formalism, where the mode functions (when written in the conventional plane wave basis) are not orthogonal, but can be correlated [30,31]. In future we hope to extend the results of this paper by studying the inhomogeneous vacuum and the ensuing non-trivially correlated cosmology.…”

Classical and Quantum Exact Solutions for a FRW Multiscalar Field Cosmology with an Exponential Potential Driven Inflation

“…The hypothesis of primordial anisotropy at early stages of the universe, and even predating inflation, is an enticing proposal that can shed some light in the anomalies found in the cosmic microwave background anisotropies on large angular scales, some serious attempts have been made [30][31][32][33], where anisotropic cosmological models, mainly the Bianchi type I model, have been employed as a spacetime background in an early anisotropic but homogenus universe that experiences an isotropization at the onset of inflation, however, traces of such anisotropies would lead to the anomalies found in the thermal maps of the cosmic microwave background. In the post inflationary evolution the universe tends towards a Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime, therefore, the standard picture of the evolution of the universe is recovered.…”

Hamiltonian theory of classical and quantum gauge invariant perturbations in Bianchi I spacetimes

“…These works correctly pointed out that the main observational features of an anisotropic phase are expected for large angular scales in the CMB in the form of anisotropic power spectra and cross-correlations between scalar and tensor perturbations (see Ref. [6] for a recent summary. )…”

“…But in the absence of anisotropic sources, the contribution of anisotropic stresses to Einstein's equations fall off with the expansion significantly faster than the contributions from radiation, matter, or a cosmological constant. Consequently, an inflationary phase of exponential expansion is very efficient in washing anisotropies away (see [2][3][4][5][6][7][8] and references therein). This fact simplifies enormously the analysis of the generation of the primordial perturbations during inflation, since one can safely neglect anisotropic aspects of the spacetime and work in the much simpler Friedmann-Lemaître-Robertson-Walker (FLRW) scenario.…”