Dark radiation and the CMB bispectrum

Non-Gaussianities in the cosmic microwave background maps arising from correlations between lensing and time variations of the gravitational potential (the so-called integrated Sachs-Wolfe effect) are one of the most important contaminants to the determination of the primordial inflationary bispectrum and may bias its determination. The presence of an extra dark radiation component, as suggested by some recent osmic microwave background measurements from the South Pole Telescope, could bias the expected value of the local bispectrum. In this paper we investigate the impact of dark radiation on the local bispectrum. As a by-product we also quantify the additional information on the dark radiation component that could come from a future precise measurement of the lensing-integrated-Sachs-Wolfe bispectrum.