Generating $\fnl$ at $\ell\lsim 60$

TL;DR

This paper discusses the generation of non-Gaussianity parameter nl at large angular scales in the CMB, revisiting theoretical bounds and their compatibility with observational data.

Contribution

It revisits the lower bound on nl generated by super-horizon perturbations in curvaton models and highlights the need for re-analysis of current data.

Findings

Lower bound on nl may be compatible with data

Re-analysis of observational data is necessary

Implications for understanding large-scale CMB anomalies

Abstract

The CMB anisotropy at $\ell\lsim 60$ seems to have some special features which include (i) a dipole modulation and (ii) a decrease in power. It is known that both of these effects can be generated if a curvaton-type field has a super-horizon perturbation. It is also known that this will generate non-gaussianity $\fnl$ in the same range of $\ell$, whose magnitude has a lower bound coming from the magnitude of the observed CMB quadrupole. I revisit that bound in the present paper, and point out that it may or may not be compatible with current data which should therefore be re-analysed.