Violation of the Rotational Invariance in the CMB Bispectrum

TL;DR

This paper explores a specific type of statistical anisotropy in the CMB bispectrum caused by primordial non-Gaussianity from vector fields, identifying new configurations that violate rotational invariance and could be detectable in future experiments.

Contribution

It introduces new multipole configurations in the CMB bispectrum that violate rotational invariance and analyzes their potential detectability, expanding understanding of early Universe physics.

Findings

New off-diagonal bispectrum configurations identified.

Amplitude of anisotropic bispectrum can match standard configurations.

Potential for future detection of these anisotropies.

Abstract

We investigate a statistical anisotropy on the Cosmic Microwave Background (CMB) bispectrum, which can be generated from the primordial non-Gaussianity induced by quantum fluctuations of a vector field. We find new configurations in the multipole space of the CMB bispectrum given by $\ell_1 = \ell_2 + \ell_3 + 2, |\ell_2 - \ell_3| - 2$ and their permutations, which violate the rotational invariance, such as an off-diagonal configuration in the CMB power spectrum. We also find that in a model presented by Yokoyama and Soda (2008), the amplitude of the statistically anisotropic bispectrum in the above configurations becomes as large as that in other configurations such as $\ell_1 = \ell_2 + \ell_3$. As a result, it might be possible to detect these contributions in future experiments, which would give us novel information about the physics of the early Universe.