On the absence of the Boulware-Deser ghost in novel graviton kinetic terms

Using novel nonlinear kinetic terms for gravitons, a large class of bi-gravity models were constructed, which are potentially free of the Boulware-Deser (BD) ghost. In this work, we derive their Hamiltonians using the ADM formalism, and verify that the BD ghost is eliminated by additional constraints. The general Hamiltonian structure is analogous to that of the other class of bi-gravity models free of the BD ghost.