Impact of post-Born lensing on the CMB

Pratten, Geraint and Lewis, Antony (2016) Impact of post-Born lensing on the CMB. Journal of Cosmology and Astroparticle Physics, 2016 (8). 047-047. ISSN 1475-7516

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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 lesssim 0.2% level on accessible scales, and that this correction and the field rotation are negligible for observations with arcminute beam and noise levels gsim 1 μK arcmin. The field rotation generates ~ 2.5% of the total lensing B-mode polarization amplitude (0.2% 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 Lt 1 μK arcmin, but its bispectrum with the convergence may be observable at ~ 3σ 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.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Research Centres and Groups: Astronomy Centre
Subjects: Q Science > QB Astronomy
Depositing User: Richard Chambers
Date Deposited: 13 Jan 2017 14:57
Last Modified: 25 Aug 2017 02:42

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Project NameSussex Project NumberFunderFunder Ref
Precision cosmological parameters : CosmoParsG1365EUROPEAN UNION616170 ERC-2013-CoG
Astrophysics and Cosmology - Sussex Consolidated GrantG1291STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/L000652/1