Probing dark energy with the cosmic microwave background: projected constraints from the Wilkinson Microwave Anisotropy Probe and Planck

We investigate the accuracy attainable by forthcoming space-based observations of the cosmic microwave background (CMB) temperature and polarization anisotropy in constraining the dark energy density parameter $\Oq$ and equation of state $\wq=p_{\rm Q}/\rho_{\rm Q}$. Despite degeneracies among parameters, it is possible for high precision observations such as those from the {\it Wilkinson Microwave Anisotropy Probe} and {\it Planck} to provide interesting information on the nature of the dark energy. Furthermore, we show that imposing a flat universe constraint makes it possible to obtain tight limits in the space of dark energy parameters even from the CMB alone.