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 parameterize by w_Q. We conclude that the dataset 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 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.