Holography in asymptotically fiat spacetimes and the BMS group

In a previous paper (Arcioni G and Dappiaggi C 2003 Preprint hep-th/0306142) we have started to explore the holographic principle in the case of asymptotically flat spacetimes and analysed, in particular, different aspects of the Bondi-Metzner-Sachs (BMS) group, namely the asymptotic symmetry group of any asymptotically flat spacetime. We continue this investigation in this paper. Having in mind an S-matrix approach with future and past null infinity playing the role of holographic screens on which the BMS group acts, we connect the IR sectors of the gravitational field with the. representation theory of the BMS group. We analyse the (complicated) mapping-between bulk and boundary symmetries pointing out differences with respect to the anti-de Sitter (AdS)/ CFT set up. Finally, we construct a BMS phase space and a free Hamiltonian for fields transforming with respect to BMN representations. The last step is supposed to be an explorative investigation of the boundary data living on the degenerate null manifold at infinity.