Boundary dynamics of asymptotically flat 3D gravity coupled to higher spin fields

Understand

We construct a two-dimensional action principle invariant under a spin-three extension of BMS$_3$ group.

• Such a theory is obtained through a reduction of Chern-Simons action with a boundary.
• This procedure is carried out by imposing a set of boundary conditions obtained from asymptotically flat spacetimes in three dimensions.
• When implementing part of this set, we obtain an analog of chiral WZW model based on a contraction of $sl(3,\mathbb{R}) \times sl(3,\mathbb{R})$.