Hunting for Statistical Anisotropy in Tensor Modes with B-mode Observations

TL;DR

This paper explores how future CMB B-mode polarization observations could detect statistical anisotropies in primordial tensor perturbations, providing a new way to test early universe models.

Contribution

It introduces a parameterization of anisotropic tensor power spectra and assesses the detectability of anisotropy levels with upcoming B-mode experiments.

Findings

Future CMB-S4 can detect tensor anisotropy parameters around 0.1

A new parameterization for anisotropic tensor spectra is proposed

Potential to constrain early universe models through B-mode polarization

Abstract

We investigate a possibility of constraining statistical anisotropies of the primordial tensor perturbations by using future observations for the Cosmic Microwave Background (CMB) B-mode polarization. By parameterizing a statistically-anisotropic tensor power spectrum as $P_h ({\boldsymbol{k}}) = P_h (k) \sum_n g_n \cos^n \theta_{\boldsymbol{k}}$, where $\theta_{\boldsymbol{k}}$ is an angle of the direction of $\hat{k}={\boldsymbol{k}}/k$ from a preferred direction, we find that it would be possible for future B-mode observations such as CMB-S4 to detect the tensor statistical anisotropy at the level of $g_n \sim {\mathcal O} (0.1)$.