Imprint of reionization on the cosmic microwave background bispectrum

We study contributions to the cosmic microwave background (CMB) bispectrum from non-Gaussianity induced by secondary anisotropies during reionization. Large-scale structure in the reionized epoch both gravitationally lenses C MB photons and produces Doppler shifts in their temperature from scattering off electrons in infall. The resulting correlation is potentially observab le through the CMB bispectrum. The second-order Ostriker-Vishniac effect al so couples to a variety of linear secondary effects to produce a bispectrum . For the currently favored flat cosmological model with a low matter conte nt and small optical depth in the reionized epoch tau less than or similar to 0.3, however, these bispectrum contributions are well below the detectio n threshold of MAP and at or below that of Planck, given their cosmic and n oise variance limitations. At the upper end of this range, they can serve a s an extra source of noise for measurements with Planck of either primordia l nongaussianity or that induced by the correlation of gravitational lensin g with the integrated Sachs-Wolfe and the thermal Sunyaev-Zel'dovich effect s. We include a discussion of the general properties of the CMB bispectrum, its configuration dependence for the various effects, and its computation in the Limber approximation and beyond.