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, parameterized as $1 +\varpi_0 (1 +
z)^{-S}$, between the gravitational potentials conventionally appearing in the
geodesic equation and the Poisson equation. Current CMB data indicate
$\varpi_0=1.67^{+3.07}_{-1.87}$ 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 a future
CMBpol experiment should be able to improve the constraints to $\varpi_0< 0.30$
for a fiducial $\varpi_0=0$ model and independent of $S$.
