Zwei-Dreibein Gravity: A Two-Frame-Field Model of 3D Massive Gravity

We present a generally covariant and parity-invariant two-frame field (zwei-dreibein) action for gravity in three space-time dimensions that propagates two massive spin-2 modes, unitarily, and we use Hamiltonian methods to confirm the absence of unphysical degrees of freedom. We show how zwei-dreibein gravity unifies previous 3D massive gravity models and extends them, in the context of the AdS/CFT correspondence, to allow for a positive central charge consistent with bulk unitarity.