Galaxy-CMB and galaxy-galaxy lensing on large scales: sensitivity to primordial non-Gaussianity

A convincing detection of primordial non-Gaussianity in the local form of the bispectrum, whose amplitude is given by the fNL parameter, offers a powerful test of inflation. In this paper we calculate the modification of two-point cross-correlation statistics of weak lensing - galaxy-galaxy lensing and galaxy-Cosmic Microwave Background (CMB) cross-correlation - due to fNL. We derive and calculate the covariance matrix of galaxy-galaxy lensing including cosmic variance terms. We focus on large scales (l<100) for which the shape noise of the shear measurement becomes irrelevant and cosmic variance dominates the error budget. For a modest degree of non-Gaussianity, fNL=+/-50, modifications of the galaxy-galaxy lensing signal at the 10% level are seen on scales R~300 Mpc, and grow rapidly toward larger scales as \propto R^2. We also see a clear signature of the baryonic acoustic oscillation feature in the matter power spectrum at ~150 Mpc, which can be measured by next-generation lensing experiments. In addition we can probe the local-form primordial non-Gaussianity in the galaxy-CMB lensing signal by correlating the lensing potential reconstructed from CMB with high-z galaxies. For example, for fNL=+/-50, we find that the galaxy-CMB lensing cross power spectrum is modified by ~10% at l~40, and by a factor of two at l~10, for a population of galaxies at z=2 with a bias of 2. The effect is greater for more highly biased populations at larger z; thus, high-z galaxy surveys cross-correlated with CMB offer a yet another probe of primordial non-Gaussianity.