The intrinsic bispectrum of the Cosmic Microwave Background

TL;DR

This paper introduces an efficient computational method to estimate the intrinsic non-Gaussianity in the CMB caused by non-linear evolution, assessing its impact on primordial non-Gaussianity searches.

Contribution

A new, fast code for second-order Einstein-Boltzmann equations enables precise estimation of intrinsic CMB bispectrum and its bias on primordial non-Gaussianity measurements.

Findings

Intrinsic bispectrum bias on f_NL is about 0.5, below Planck sensitivity.

Including all effects except lensing and time-delay, the bias remains small.

The code's speed confirms robustness of results across numerical parameters.

Abstract

We develop a new, efficient code for solving the second-order Einstein-Boltzmann equations, and use it to estimate the intrinsic CMB non-Gaussianity arising from the non-linear evolution of density perturbations. The full calculation involves contributions from recombination and less tractable contributions from terms integrated along the line of sight. We investigate the bias that this intrinsic bispectrum implies for searches of primordial non-Gaussianity. We find that the inclusion or omission of certain line of sight terms can make a large impact. When including all physical effects but lensing and time-delay, we find that the local-type f_nl would be biased by f_nl ~ 0.5, below the expected sensitivity of the Planck satellite. The speed of our code allows us to confirm the robustness of our results with respect to a number of numerical parameters.