Three-dimensional Bondi-Metzner-Sachs invariant two-dimensional field   theories as the flat limit of Liouville theory
  In the gravitational context, Liouville theory is the two-dimensional conformal field theory that controls the boundary dynamics of asymptotically AdS_3 spacetimes at the classical level. By taking a suitable limit of the coupling constants of the Hamiltonian formulation of Liouville, we construct and analyze a BMS_3 invariant two-dimensional field theory that is likely to control the boundary dynamics at null infinity of three dimensional asymptotically flat gravity. 
Glenn Barnich, Andr\'es Gomberoff, Hern\'an A. Gonz\'alez
hep-th gr-qc