Laser Ranging Delay in the Bi-Metric Theory of Gravity
  We introduce a linearized bi-metric theory of gravity with two metrics. The metric g_{ab} describes null hypersurfaces of the gravitational field while light moves on null hypersurfaces of the optical metric \bar{g}_{ab}. Bi-metrism naturally arises in vector-tensor theories with matter being non-minimally coupled to gravity via long-range vector field. We derive explicit Lorentz-invariant solution for a light ray propagating in space-time of the bi-metric theory and disentangle relativistic effects associated with the two metrics. This anlysis can be valuable for future spaceborne laser missions ASTROD and LATOR dedicated to map various relativistic gravity parameters in the solar system to unparalleled degree of accuracy. 
Sergei M. Kopeikin (University of Missouri-Columbia, USA) and Wei-Tou   Ni (The Purple Mountain Observatory, Nanjing, China)