On Lorentz-Invariant Bispin-2 Theories

We investigate a Lorentz invariant action that is quadratic in two rank-2 symmetric tensor fields in Minkowski spacetime. We apply a scalar-vector-tensor decomposition to two tensor fields by virtue of three-dimensional rotation invariance of Minkowski spacetime and classify theories with 7 degrees of freedom based on the Hamiltonian analysis. We find two new theories, which cannot be mapped from the linearized Hassan-Rosen bigravity. In these theories, the new mass interactions can be allowed thanks to the transverse diffeomorphism invariance of action.