CMB Hemispherical Asymmetry: Long Mode Modulation and non-Gaussianity

TL;DR

This paper investigates how large-scale superhorizon modes and non-Gaussianities in the CMB can produce hemispherical asymmetry, emphasizing the importance of squeezed limit non-Gaussianity and providing a consistency condition relating asymmetry amplitude to f_NL.

Contribution

It clarifies the role of squeezed limit non-Gaussianity in hemispherical asymmetry and establishes a consistency condition linking asymmetry amplitude to f_NL.

Findings

Hemispherical asymmetry is sensitive to squeezed limit non-Gaussianity.

A consistency condition relates dipole asymmetry amplitude to f_NL.

The approach addresses previous criticisms about non-Gaussianity contributions.

Abstract

The observed hemispherical asymmetry in CMB map can be explained by modulation from a long wavelength super horizon mode which non-linearly couples to the CMB modes. We address the criticism in [1] about the role of non-Gaussianities in squeezed and equilateral configurations in generating hemispherical asymmetry from the long mode modulation. We stress that the modulation is sensitive to the non-Gaussianity in the squeezed limit. In addition, we demonstrate the validity of our approach in providing a consistency condition relating the amplitude of dipole asymmetry to f_{NL} in the squeezed limit.