Summary: We show that the large limit of certain conformal field theories in various dimensions include in their Hilbert space of sector describing supergravity on the product of anti-de Sitter spacetimes, spheres and other compact manifolds. This is shown by taking some branes in the full M resp. string theory and then taking a low energy limit where the field theory on the brane decouples from the bulk.
We observe that, in this limit, we can still trust the near horizon geometry for large . The enhanced supersymmetries of the near horizon geometry correspond to the extra supersymmetry generators present in the superconformal group (as opposed to just the super-Poincaré group). The ’t Hooft limit of super-Yang-Mills at the conformal point is shown to contain strings: they are IIB strings.
We conjecture that compactifications of M resp. string theory on various anti-de Sitter spacetimes is dual to various conformal field theories. This leads to a new proposal for a definition of M-theory which could be extended to include five noncompact dimensions.