The cosmic microwave background bispectrum from the non-linear evolution of the cosmological perturbations

TL;DR

This paper computes the complete second-order bispectrum of the CMB temperature anisotropies, including all cosmic fluids and effects, providing new insights into non-linear evolution and its impact on primordial non-Gaussianity detection.

Contribution

It presents the first full computation of the CMB bispectrum from non-linear evolution, including neutrinos and second order effects, with results expressed in terms of fNL for various configurations.

Findings

Non-linear effects produce a bispectrum signal equivalent to fNL~5 at lmax=2000.

Comparison with previous analytical regimes validates the comprehensive computation.

Results inform the interpretation of primordial non-Gaussianity measurements.

Abstract

This article presents the first computation of the complete bispectrum of the cosmic microwave background temperature anisotropies arising from the evolution of all cosmic fluids up to second order, including neutrinos. Gravitational couplings, electron density fluctuations and the second order Boltzmann equation are fully taken into account. Comparison to limiting cases that appeared previously in the literature are provided. These are regimes for which analytical insights can be given. The final results are expressed in terms of equivalent fNL for different configurations. It is found that for moments up to lmax=2000, the signal generated by non-linear effects is equivalent to fNL~5 for both local-type and equilateral-type primordial non-Gaussianity.