Dark energy and cosmic microwave background bispectrum

We compute the cosmic microwave background bispectrum arising from the cross-correlation of primordial, lensing, and Rees-Sciama signals. The amplitude of the bispectrum signal is sensitive to the matter density parameter Omega(0) and the equation of state of the dark energy, which we parametrize by w(Q). We conclude that the data set of the Atacama Cosmology Telescope, combined with MAP 2-year data, or the Planck data Set alone will allow us to break the degeneracy between Omega(0) and w(Q) that arises from the analysis of the CmB power spectrum. In particular a joint measurement of Omega(0) and w(Q) with 10% and 30% error on the two parameters, respectively, at the 90% confidence level can realistically be achieved.