The CMB asymmetry from inflation

TL;DR

This paper investigates the potential of large-scale perturbations in inflation models to explain the observed CMB asymmetry, finding that curvaton fields could produce the required asymmetry with specific non-Gaussianity parameters.

Contribution

It refines previous calculations by analyzing the CMB asymmetry in various inflation scenarios using current data, highlighting the curvaton model's potential to explain the asymmetry.

Findings

Inflaton models likely produce too small asymmetry.

Curvaton models can produce observable asymmetry with specific non-Gaussianity.

The required non-Gaussianity parameters could be tested with existing CMB data.

Abstract

Erickcek, Kamionkowski and Carroll proposed in 2008 that the dipole modulation of the CMB could be due to a very large scale perturbation of the field $\phi$ causing the primordial curvature perturbation. We repeat their calculation using weaker assumptions and the current data. If $\phi$ is the inflaton of {\em any} single-field inflation with the attractor behaviour, the asymmetry is almosy certainly too small. If instead $\phi$ is {\em any} curvaton-type field (ie.\ one with the canonical kinetic term and a negligible effect during inflation) the asymmetry can agree with observation if $|\fnl|$ in the equilateral configuration is $\simeq 10$ for $k\mone=1\Gpc$ and $\lsim 3$ for $k\mone=1\Mpc$. An $\fnl$ with these properties can apparently be obtained from the curvaton with an axionic potential. Within any specific curvaton-type model, the function $\fnl(k_1,k_2,k_3)$ required to generate the asymmetry would be determined, and could perhaps already be confirmed or ruled out using existing Planck or WMAP data.