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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 Regan
Squeezed 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.

History

Publication status

  • Published

Journal

Journal of Cosmology and Astroparticle Physics

ISSN

1475-7516

Publisher

Institute of Physics

Issue

3

Volume

12

Department affiliated with

  • Physics and Astronomy Publications

Full text available

  • No

Peer reviewed?

  • Yes

Legacy Posted Date

2012-11-07

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