期刊
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
卷 -, 期 6, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/1475-7516/2012/06/023
关键词
non-gaussianity; cosmological perturbation theory; CMBR theory; gravitational lensing
资金
- Science and Technology Facilities Council [ST/I000976/1]
- STFC [ST/I000976/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/I000976/1] Funding Source: researchfish
- UK Space Agency [ST/H00002X/1] Funding Source: researchfish
The small-scale CMB temperature we observe on the sky is modulated by perturbations that were super-horizon at recombination, giving differential focussing and lensing that generate a non-zero bispectrum even for single-field inflation where local physics is identical. Understanding this signal is important for primordial non-Gaussianity studies and also parameter constraints from the CMB lensing bispectrum signal. Because of cancellations individual effects can appear larger or smaller than they are in total, so a full analysis may be required to avoid biases. I relate angular scales on the sky to physical scales at recombination using the optical equations, and give full-sky results for the large-scale adiabatic temperature bispectrum from Ricci focussing (expansion of the ray bundle), Weyl lensing (convergence and shear), and temperature redshift modulations of small-scale power. The delta N expansion of the beam is described by the constant temperature 3-curvature, and gives a nearly-observable version of the consistency relation prediction from single-field inflation. I give approximate arguments to quantify the likely importance of dynamical effects, and argue that they can be neglected for modulation scales l less than or similar to 100, which is sufficient for lensing studies and also allows robust tests of local primordial non-Gaussianity using only the large-scale modulation modes. For accurate numerical results early and late-time ISW effects must be accounted for, though I confirm that the late-time non-linear Rees-Sciama contribution is negligible compared to other more important complications. The total corresponds to f(NL) similar to 7 for Planck-like temperature constraints and f(NL) similar to 11 for cosmic-variance limited data to l(max) = 2000. Temperature lensing bispectrum estimates are affected at the 0.2 sigma level by Ricci focussing, and up to 0.5 sigma with polarization.
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