Spectral Flow and Flat Space Holography in 3D
Over the course of the last 20 years the holographic principle has lead to many new insights regarding certain aspects of quantum gravity. Originally formulated in the context of string theory and Anti-de Sitter spacetimes a reasonable question to as is: "How general is the holographic principle?". As such it is interesting to find possible ways to extend the holographic principle also to spacetimes that are not Anti-de Sitter. One particularly interesting setting for such an extension is to consider asymptotically flat spacetimes in 3D as dual gravitational theories that allows for a wide range of tests for a possible new holographic correspondence. In this talk I present new boundary conditions (supersymmetric as well as non-supersymmetric ones) for asymptotically flat spacetimes in 3D that exhibit a spectral flow symmetry. I first describe the general algorithm underlying the procedure of choosing boundary conditions and subsequently determining the underlying symmetries of a possible holographic dual quantum field theory. I then present the aforementioned supersymmetric and non-supersymmetric gravity models as well as corresponding novel boundary conditions that exhibit spectral flow symmetry and discuss their physical interpretation. A special focus will be on a spectral flow invariant Cardy-like formula for cosmological solutions in flat space, how the spectral flow affects a states in the (proposed) dual quantum field theory and the connection between supersymmetry and spectral flow in asymptotically flat spacetimes.