Impact of polarization on the intrinsic cosmic microwave background bispectrum

We compute the cosmic microwave background (CMB) bispectrum induced by the evolution of the primordial density perturbations, including for the first time both temperature and polarization using a second-order Boltzmann code. We show that including polarization can increase the signal-to-noise by a factor 4 with respect to temperature alone. We find the expected signal-to-noise for this intrinsic bispectrum of S=N 1⁄4 3.8; 2.9; 1.6 and 0.5 for an ideal experiment with an angular resolution of lmax 1⁄4 3000, the proposed CMB surveys PRISM and COrE, and Planck’s polarized data, respectively; the bulk of this signal comes from E-mode polarization 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 fintr NL 1⁄4 0.66 for an ideal experiment with lmax 1⁄4 3000. Finally, we verify the robustness of our results by recovering the analytic approximation for the squeezed-limit bispectrum in the general polarized case.