Level Of Statistical Anisotropy Research Articles

The TT, TB, EB and BB correlations in anisotropic inflation

The ongoing and future experiments will measure the B-mode from different sky coverage and frequency bands, with the potential to reveal non-trivial features in polarization map. In this work we study the TT, TB, EB and BB correlations associated with the B-mode polarization of CMB map in models of charged anisotropic inflation. The model contains a chaotic-type large field complex inflaton which is charged under the U(1) gauge field. We calculate the statistical anisotropies generated in the power spectra of the curvature perturbation, the tensor perturbation and their cross-correlation. It is shown that the asymmetry in tensor power spectrum is a very sensitive probe of the gauge coupling. While the level of statistical anisotropy in temperature power spectrum can be small and satisfy the observational bounds, the interactions from the gauge coupling can induce large directional dependence in tensor modes. This will leave interesting anisotropic fingerprints in various correlations involving the B-mode polarization such as the TB cross-correlation which may be detected in upcoming Planck polarization data. In addition, the TT correlation receives an anisotropic contribution from the tensor sector which naturally decays after l ≳ 100. We expect that the mechanism of using tensor sector to induce asymmetry at low l to be generic which can also be applied to address other low l CMB anomalies.

Non-gaussianity from the trispectrum and vector field perturbations

We use the δN formalism to study the trispectrum Tζ of the primordial curvature perturbation ζ when the latter is generated by vector field perturbations, considering the tree-level and one-loop contributions. The order of magnitude of the level of non-gaussianity in the trispectrum, τNL, is calculated in this scenario and related to the order of magnitude of the level of non-gaussianity in the bispectrum, fNL, and the level of statistical anisotropy in the power spectrum, gζ. Such consistency relations will put under test this scenario against future observations. Comparison with the expected observational bound on τNL from WMAP, for generic inflationary models, is done.

Simple types of anisotropic inflation

We display some simple cosmological solutions of gravity theories with quadratic Ricci curvature terms added to the Einstein-Hilbert Lagrangian which exhibit anisotropic inflation. The Hubble expansion rates are constant and unequal in three orthogonal directions. We describe the evolution of the simplest of these homogeneous and anisotropic cosmological models from its natural initial state and evaluate the deviations they will create from statistical isotropy in the fluctuations produced during a period of anisotropic inflation. The anisotropic inflation is not a late-time attractor in these models but the rate of approach to a final isotropic de Sitter state is slow and is conducive to the creation of observable anisotropic statistical effects in the microwave background. The statistical anisotropy would not be scale invariant and the level of statistical anisotropy will grow with scale.

Non-Gaussianity at tree and one-loop levels from vector field perturbations

We study the spectrum ${\mathcal{P}}_{\ensuremath{\zeta}}$ and bispectrum ${B}_{\ensuremath{\zeta}}$ of the primordial curvature perturbation $\ensuremath{\zeta}$ when the latter is generated by scalar and vector field perturbations. The tree-level and one-loop contributions from vector field perturbations are worked out considering the possibility that the one-loop contributions may be dominant over the tree-level terms [both (either) in ${\mathcal{P}}_{\ensuremath{\zeta}}$ and (or) in ${B}_{\ensuremath{\zeta}}$] and vice versa. The level of non-Gaussianity in the bispectrum, ${f}_{\mathrm{NL}}$, is calculated and related to the level of statistical anisotropy in the power spectrum, ${g}_{\ensuremath{\zeta}}$. For very small amounts of statistical anisotropy in the power spectrum, the level of non-Gaussianity may be very high, in some cases exceeding the current observational limit.