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CMB lensing and primordial squeezed non-gaussianity
journal contribution
posted on 2023-06-08, 12:43 authored by Ruth Pearson, Antony LewisAntony Lewis, Donough ReganSqueezed primordial non-Gaussianity can strongly constrain early-universe physics, but it can only be observed on the CMB after it has been gravitationally lensed. We give a new simple non-perturbative prescription for accurately calculating the effect of lensing on any squeezed primordial bispectrum shape, and test it with simulations. We give the generalization to polarization bispectra, and discuss the effect of lensing on the trispectrum. We explain why neglecting the lensing smoothing effect does not significantly bias estimators of local primordial non-Gaussianity, even though the change in shape can be >~10%. We also show how tau_NL trispectrum estimators can be well approximated by much simpler CMB temperature modulation estimators, and hence that there is potentially a ~10-30% bias due to very large-scale lensing modes, depending on the range of modulation scales included. Including dipole sky modulations can halve the tau_NL error bar if kinematic effects can be subtracted using known properties of the CMB temperature dipole. Lensing effects on the g_NL trispectrum are small compared to the error bar. In appendices we give the general result for lensing of any primordial bispectrum, and show how any full-sky squeezed bispectrum can be decomposed into orthogonal modes of distinct angular dependence.
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Publication status
- Published
Journal
Journal of Cosmology and Astroparticle PhysicsISSN
1475-7516Publisher
Institute of PhysicsPublisher URL
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3Volume
12Department affiliated with
- Physics and Astronomy Publications
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- No
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- Yes
Legacy Posted Date
2012-11-07Usage metrics
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