  The effects of vacuum polarization arising from loops of massive scalar
particles on graviton propagation in curved space are considered. Physically,
they are due to curvature induced tidal forces acting on the cloud of virtual
scalar particles surrounding the graviton. The effects are tractable in a WKB
and large mass limit and the results can be written as an effective refractive
index for the graviton modes with both a real and imaginary part. The imaginary
part of the refractive index is a curvature induced contribution to the
wavefunction renormalization of the graviton in real affine time and can have
the effect of dressing or un-dressing the graviton. The real part of the
refractive index increases logarithmically at high frequency as long as the
null energy condition is satisfied by the background.
