Abstract
We calculate the cosmic microwave background (CMB) bispectrum due to inhomogeneous reionization. We calculate all the terms that can contribute to the bispectrum that are products of first-order terms on all scales in conformal Newtonian gauge. We also correctly account for the de-correlation between the matter density and initial conditions using perturbation theory up to third order. We find that the bispectrum is of local type as expected. For a reasonable model of reionization, in which the universe is completely ionized by redshift zri ∼ 8 with optical depth to the last scattering surface τ0 = 0.087, the signal-to-noise ratio (S/N) for detection of the CMB temperature bispectrum is S/N ∼ 0.1 and confusion in the estimation of primordial non-Gaussianity is fNL ∼ −0.1. For an extreme model with zri ∼ 12.5 and τ0 = 0.14, we get S/N ∼ 0.5 and fNL ∼ −0.2.
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