Near Horizon Boundary Conditions for Spin-3 Gravity in Flat Space
In field theories the physical content of the theory is given by the field equations and the boundary conditions. While it is common practice in non-gravitational theories to demand that the fields asymptotically vanish at the boundary of spacetime, boundary conditions for theories of gravity are quite subtle. Recently (2015/2016), three different groups (Donnay et al, Afshar et al and Hawking et al) asked the question whether boundary conditions can be formulated for the near horizon region of non-extremal black holes in a sensible way. In this talk I review the extension of the boundary conditions of Afshar et al to higher-spin gravity in three-dimensional flat space. We find that the near horizon symmetries are governed by a surprisingly simple algebra and that there seems to be a universal expression for the entropy of (higher-spin) black holes/flat space cosmologies in terms of the near horizon charges in three dimensions.