The Microwave Background Bispectrum, Paper I: Basic Formalism
  In this paper, we discuss the potential importance of measuring the CMB anisotropy bispectrum. We develop a formalism for computing the bispectrum and for measuring it from microwave background maps. As an example, we compute the bispectrum resulting from the 2nd order Rees-Sciama effect, and find that is undetectable with current and upcoming missions. 
David N. Spergel and David M. Goldberg (Princeton University   Observatory)