Alan Guth, Cosmology, 8.962 Lecture 26, May 16, 2018, p. 1.

8.962 Lecture 26

May 16, 2018

COSMOLOGY

Ripples in the Cosmic Microwave Background

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Spectrum of CMB Ripples

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Planck 2015 TE Power Spectrum

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Alan Guth, Cosmology, 8.962 Lecture 26, May 16, 2018, p. 2.

Planck 2015 EE Power Spectrum

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Gaussianity of the CMB

Nongaussianites are measured by fNL, where Planck 2015 set thebounds

f localNL = 0.8± 5.0 ,

f equilNL = −4± 43 ,

forthoNL = −26± 21 (68% CL statistical).

Local, equil, and ortho refer to three different “shapes” for the3-point function (bispectrum). fNL is defined by

Φ = Φg + fNLΦ2g ,

where Φ is the Bardeen potential. Note that the nongaussian termwill be comparable to the gaussian term when fNL ∼ 105, so thelimits imply that the CMB is VERY gaussian.

Alan Guth

Massachusetts Institute of Technology

8.962 Lecture 26, May 16, 2018 –5–