paper

Impact of post-Born lensing on the CMB

arXiv:1605.05662 · doi:10.1088/1475-7516/2016/08/047

Abstract

Lensing of the CMB is affected by post-Born lensing, producing corrections to the convergence power spectrum and introducing field rotation. We show numerically that the lensing convergence power spectrum is affected at the level on accessible scales, and that this correction and the field rotation are negligible for observations with arcminute beam and noise levels . The field rotation generates of the total lensing B-mode polarization amplitude ( in power on small scales), but has a blue spectrum on large scales, making it highly subdominant to the convergence B modes on scales where they are a source of confusion for the signal from primordial gravitational waves. Since the post-Born signal is non-linear, it also generates a bispectrum with the convergence. We show that the post-Born contributions to the bispectrum substantially change the shape predicted from large-scale structure non-linearities alone, and hence must be included to estimate the expected total signal and impact of bispectrum biases on CMB lensing reconstruction quadratic estimators and other observables. The field-rotation power spectrum only becomes potentially detectable for noise levels , but its bispectrum with the convergence may be observable at with Stage IV observations. Rotation-induced and convergence-induced B modes are slightly correlated by the bispectrum, and the bispectrum also produces additional contributions to the lensed BB power spectrum.

26 pages, 11 figures, 1 table. Sign change in Eq 5.2 corrects sign of correlation bispectrum in Eq 5.7 & Fig. 11. Footnote on page 15 justifying the treatment of polarization rotation, based on the recent analysis in arXiv:1706.02673. Footnote for Table I page 14 stating Lmax used was 4000. Footnote pg. 10 added. Fixed sign in Eq 2.8

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