Bulk and Boundary Unitary Gravity in 3D: MMG$_2$

Understand

We construct a massive spin-2 theory in 2+1 dimensions that is immune to the bulk-boundary unitarity conflict in anti-de Sitter space and hence amenable to holography.

• The theory is an extension of Topologically Massive Gravity, just like the recently found Minimal Massive Gravity (MMG), but it has two massive helicity modes instead of a single one.
• The theory admits all the solutions of TMG with a redefined topological parameter.
• We calculate the Shapiro time-delay and show that flat-space (local) causality is not violated.