Mass eigenstates in bimetric theory with matter coupling

Understand

In this paper we study the ghost-free bimetric action extended by a recently proposed coupling to matter through a composite metric.

• The equations of motion for this theory are derived using a method which avoids varying the square-root matrix that appears in the matter coupling.
• We make an ansatz for which the metrics are proportional to each other and find that it can solve the equations provided that one parameter in the action is fixed.
• In this case, the proportional metrics as well as the effective metric that couples to matter solve Einstein's equations of general relativity including a matter source.