On the non-Gaussianity from Recombination

TL;DR

This paper estimates the non-Gaussian signal in the CMB caused by non-linear effects during recombination, highlighting its impact on primordial non-Gaussianity measurements.

Contribution

It provides the first estimate of the non-Gaussianity level from recombination effects, crucial for interpreting CMB non-Gaussian signals.

Findings

Recombination induces a non-Gaussian signal mainly in the equilateral configuration.

This signal can bias measurements of primordial non-Gaussianity, shifting the detection threshold.

The contamination could be significant for experiments like Planck, affecting the minimum detectable f_NL.

Abstract

The non-linear effects operating at the recombination epoch generate a non-Gaussian signal in the CMB anisotropies. Such a contribution is relevant because it represents a major part of the second-order radiation transfer function which must be determined in order to have a complete control of both the primordial and non-primordial part of non-Gaussianity in the CMB anisotropies. We provide an estimate of the level of non-Gaussianity in the CMB arising from the recombination epoch which shows up mainly in the equilateral configuration. We find that it causes a contamination to the possible measurement of the equilateral primordial bispectrum shifting the minimum detectable value of the non-Gaussian parameter f^equil_NL by Delta f^equil_NL= O(10) for an experiment like Planck.