Limits of dark energy measurements from correlations of CMB lensing, the integrated Sachs-Wolfe effect, and galaxy counts

I discuss several issues that arise when trying to constrain the dark energy equation of state using correlations of the integrated Sachs-Wolfe effect with galaxy counts and lensing of the cosmic microwave background. These techniques are complementary to others such as galaxy shear surveys, and can use data that will already be obtained from currently planned observations. In regimes where cosmic variance and shot noise are the dominant sources of error, constraints could be made on the mean equation of state to ±0.33 and its first derivative to ±1.0. Perhaps more interesting is that the determination of dark energy parameters by these types of experiments depends strongly on the presence or absence of perturbations in the dark energy fluid