World-Sheet formulation of M theory
  We first review the interpretation of world-sheet defects as $D$ branes described by a critical theory in 11 dimensions, that we interpret as $M$ theory. We then show that $D$-brane recoil induces dynamically an anti-de-Sitter (AdS) space-time background, with criticality restored by a twelfth time-like dimension described by a Liouville field. Local physics in the bulk of this AdS$_{11}$ may be described by an $Osp(1|32,R) \otimes Osp(1|32,R)$ topological gauge theory (TGT), with non-local boundary states in doubleton representations. We draw analogies with structures previously exhibited in two-dimensional black-hole models. Wilson loops of `matter' in the TGT may be described by an effective string action, and defect condensation may yield string tension and cause a space-time metric to appear. 
John Ellis, N.E. Mavromatos and D.V. Nanopoulos