A link between ghost-free bimetric and Eddington-inspired Born-Infeld theory

Understand

We provide an auxiliary field formulation of the full ghost-free bimetric theory which avoids the explicit presence of a square-root matrix in the action.

• This description always allows for a branch of solutions where the auxiliary fields can be integrated out to give back the ghost-free theory.
• For certain parameter regions the two formulations are dynamically equivalent, but in the general case another branch of solutions also exists.
• We show that this second branch, with certain restrictions on the parameters of the theory, is dynamically equivalent to Eddington-inspired Born-Infeld gravity.