Generating the cosmic microwave background power asymmetry with $g_{NL}$

TL;DR

This paper explores how a higher-order term involving $g_{NL}$ in the $ abla N$ formalism can generate CMB power asymmetry without large $f_{NL}$, linking isocurvature fields and non-Gaussianity constraints.

Contribution

It introduces a novel mechanism using $g_{NL}$ to produce CMB asymmetry, relaxing the need for large $f_{NL}$ and analyzing parameter constraints.

Findings

The $g_{NL}$ term can generate asymmetry without large $f_{NL}$.

Isocurvature field contribution must be subdominant to inflaton.

Constraints define an allowed $f_{NL}-g_{NL}$ parameter space.

Abstract

We consider a higher order term in the $\delta N$ expansion for the CMB power asymmetry generated by a superhorizon isocurvature field fluctuation. The term can generate the asymmetry without requiring a large value of $f_{NL}$. Instead it produces a non-zero value of $g_{NL}$. A combination of constraints lead to an allowed region in $f_{NL}-g_{NL}$ space. To produce the asymmetry with this term without a large value of $f_{NL}$ we find that the isocurvature field needs to contribute less than the inflaton towards the power spectrum of the curvature perturbation.