Bayesian Limits on Primordial Isotropy Breaking

TL;DR

This paper tests the assumption of primordial isotropy in the universe's initial conditions by analyzing WMAP data, setting bounds on deviations, and finding no significant evidence for anisotropy.

Contribution

It provides model-independent bounds on deviations from primordial isotropy using WMAP data, a novel approach in testing early universe assumptions.

Findings

No significant evidence for primordial isotropy breaking

Quadrupole deviations are constrained to be subdominant

Limits set on the amplitude of primordial spectrum quadrupole

Abstract

It is often assumed that primordial perturbations are statistically isotropic, which implies, among other properties, that their power spectrum is invariant under rotations. In this article, we test this assumption by placing model-independent bounds on deviations from rotational invariance of the primordial spectrum. Using five-year WMAP cosmic microwave anisotropy maps, we set limits on the overall norm and the amplitude of individual components of the primordial spectrum quadrupole. We find that there is no significant evidence for primordial isotropy breaking, and that an eventually non-vanishing quadrupole has to be subdominant.