Flat-space scattering and bulk locality in the AdS-CFT correspondence

The large radius limit in the AdS-CFT correspondence is expected to provide a holographic derivation of flat-space scattering amplitudes. This suggests that questions of locality in the bulk should be addressed in terms of properties of the S matrix and their translation into the conformal field theory. There are, however, subtleties in this translation related to generic growth of amplitudes near the boundary of anti--de Sitter space. Flat space amplitudes are recovered after a delicate projection of CFT correlators onto normal-mode frequencies of AdS. Once such amplitudes are obtained from the CFT, possible criteria for approximate bulk locality include bounds on growth of amplitudes at high energies and reproduction of semiclassical gravitational scattering at long distances.