paper

Effect of lensing non-Gaussianity on the CMB power spectra

arXiv:1608.01263 · doi:10.1088/1475-7516/2016/12/003

Abstract

Observed CMB anisotropies are lensed, and the lensed power spectra can be calculated accurately assuming the lensing deflections are Gaussian. However, the lensing deflections are actually slightly non-Gaussian due to both non-linear large-scale structure growth and post-Born corrections. We calculate the leading correction to the lensed CMB power spectra from the non-Gaussianity, which is determined by the lensing bispectrum. The lowest-order result gives corrections to the BB and EE polarization spectra on small-scales, however we show that the effect on EE is reduced by about a factor of two by higher-order Gaussian lensing smoothing, rendering the total effect safely negligible for the foreseeable future. We give a simple analytic model for the signal expected from skewness of the large-scale lensing field; the effect is similar to a net demagnification and hence a small change in acoustic scale (and therefore out of phase with the dominant lensing smoothing that predominantly affects the peaks and troughs of the power spectrum).

10 pages, 5 figures. Minor update to JCAP version, correcting sign of Omega term in Eq 2.7 and hence the sign of the correlation bispectrum (with very small effect on numerical result)

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