CMB lensing and primordial non-Gaussianity

TL;DR

This paper investigates how gravitational lensing affects the estimation of primordial non-Gaussianity in the CMB, finding minimal impact on constraints for a Planck-like experiment when biases are properly accounted for.

Contribution

It demonstrates that lensing does not significantly degrade non-Gaussianity constraints for Planck-like data if biases are understood, and validates low-order approximations with simulations.

Findings

Lensing causes a smoothing of the CMB bispectrum similar to the power spectrum.

No significant degradation in fNL constraints for Planck-like experiments when biases are managed.

Low-order Taylor approximations are validated for the lensed bispectrum and biases.

Abstract

We study the effects of gravitational lensing on the estimation of non-Gaussianity from the bispectrum of the cosmic microwave background (CMB) temperature anisotropies. We find that the effect of lensing on the bispectrum may qualitatively be described as a smoothing of the acoustic features analogous to the temperature power spectrum. In contrast to previous results, for a Planck-like experiment which is cosmic-variance limited to L=2000, we find that lensing causes no significant degradation of our ability to constrain the non-Gaussianity amplitude fNL for both local and equilateral configurations, provided that the biases due to the cross correlation between the lensing potential and the integrated-Sachs-Wolfe (ISW) contribution to the CMB temperature are adequately understood. With numerical simulations, we also verify that low-order Taylor approximations to the lensed bispectrum and ISW-lensing biases are accurate.