Papers › Impact of polarisation on the intrinsic CMB bispectrum
Impact of polarisation on the intrinsic CMB bispectrum
Guido W. Pettinari, Christian Fidler, Robert Crittenden, Kazuya Koyama, Antony Lewis, David Wands
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We compute the bispectrum induced in the cosmic microwave background (CMB) temperature and polarisation by the evolution of the primordial density perturbations using the second-order Boltzmann code SONG. We show that adding polarisation increases the signal-to-noise ratio by a factor four with respect to temperature alone and we estimate the observability of this intrinsic bispectrum and the bias it induces on measurements of primordial non-Gaussianity. When including all physical effects except the late-time non-linear evolution, we find for the intrinsic bispectrum a signal-to-noise of S/N=3.8, 2.9, 1.6 and 0.5 for, respectively, an ideal experiment with an angular resolution of ℓₘₐₓ=3000, the proposed CMB surveys PRISM and COrE, and Planck's polarised data; the bulk of this signal comes from the E-polarisation and from squeezed configurations. We discuss how CMB lensing is expected to reduce these estimates as it suppresses the bispectrum for squeezed configurations and contributes to the noise in the estimator. We find that the presence of the intrinsic bispectrum will bias a measurement of primordial non-Gaussianity of local type by f_(NL)ᵇⁱᵃˢ=0.66 for an ideal experiment with ℓₘₐₓ=3000. Finally, we verify the robustness of our results by reproducing the analytical approximation for the squeezed-limit bispectrum in the general polarised case.
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