Post-Newtonian parameter $\gamma$ and the deflection of light in ghost-free massive bimetric gravity

Understand

We consider the parametrized post-Newtonian (PPN) limit of ghost-free massive bimetric gravity with two mutually non-interacting matter sectors coupled to the two metrics.

• Making use of a gauge-invariant differential decomposition of the metric perturbations, we solve the field equations up to the linear PPN order for a static, point-like mass source.
• From the result we derive the PPN parameter $\gamma$ for spherically symmetric systems, which describes the gravitational deflection of light by visible matter.
• By a comparison to its value measured in the solar system we obtain bounds on the parameters of the theory.