AdS / CFT correspondence and topological field theory

In = 4 super Yang-Mills theory on a four-manifold M, one can specify a discrete magnetic flux valued in H2(M,N). This flux is encoded in the AdS/CFT correspondence in terms of a five-dimensional topological field theory with Chern-Simons action. A similar topological field theory in seven dimensions governs the space of ``conformal blocks'' of the six-dimensional (0,2) conformal field theory.