Lensed cosmic microwave background constraints on post-general-relativity parameters

The constraints on departures from general relativity (GR) at cosmological length scales due to cosmic microwave background (CMB) data are discussed. The departure from GR is measured by the ratio, parametrized as 1+pi(0)(1+z)(-S), between the gravitational potentials conventionally appearing in the geodesic equation and the Poisson equation. Current CMB data indicate pi(0)=1.67(-1.87)(+3.07) at the 2 sigma confidence level, while S remains unconstrained. The departure from GR affects the lensing conversion of E-mode into B-mode polarization. Hence, the lensing measurements from CMBpol alone should be able to improve the constraint to pi(0)< 0.52 (2 sigma) for a fiducial pi(0)=0 model independent of S.