Unitary Extension of Exotic Massive 3D Gravity from Bi-gravity

Understand

We obtain a new 3D gravity model from two copies of parity-odd Einstein-Cartan theories.

• Using Hamiltonian analysis, we demonstrate that the only local degrees of freedom are two massive spin-2 modes.
• Unitarity of the model in anti-de Sitter and Minkowski backgrounds can be satisfied for vast choices of the parameters without fine-tuning.
• The recent "exotic massive 3D gravity" model arises as a limiting case of the new model.