General quadrupolar statistical anisotropy: Planck limits

TL;DR

This paper investigates complex quadrupolar statistical anisotropy in the cosmic microwave background, extending previous models by considering two multipole vectors, and uses Planck 2015 data to set limits on these anisotropies and related inflationary theories.

Contribution

It introduces a more general quadrupolar anisotropy model with two multipole vectors and constrains its amplitude using Planck data, expanding beyond previous simpler models.

Findings

Limits on quadrupolar amplitude $g_*$ for various shapes

Constraints on inflationary scenarios predicting such anisotropy

Extension of statistical anisotropy analysis beyond single-vector models

Abstract

Several early Universe scenarios predict a direction-dependent spectrum of primordial curvature perturbations. This translates into the violation of the statistical isotropy of cosmic microwave background radiation. Previous searches for statistical anisotropy mainly focussed on a quadrupolar direction-dependence characterised by a single multipole vector and an overall amplitude $g_*$. Generically, however, the quadrupole has a more complicated geometry described by two multipole vectors and $g_*$. This is the subject of the present work. In particular, we limit the amplitude $g_*$ for different shapes of the quadrupole by making use of Planck 2015 maps. We also constrain certain inflationary scenarios which predict this kind of more general quadrupolar statistical anisotropy.