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 Ω₀ 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 Ω₀ and w _Q that arises from the analysis of the CMB power spectrum. In particular a joint measurement of Ω₀ and w_Q with 10% and 30% error on the two parameters, respectively, at the 90% confidence level can realistically be achieved.