On graviton propagation in curved space-time background
  Equation describing propagation of gravitational waves (GW) over arbitrary
curved space-time background is analyzed. The new terms, which are absent in
the conventional homogeneous and isotropic Friedmann cosmology, are found. A
section where we have discussed the choice of gauge for tensor perturbations is
added. Some examples of realistic metric, where this new term manifests itself,
are presented. Possible implications to very low frequency GW are briefly
discussed.
