Chern–Simons theory
In the context of string theory, a "U"("N") Chern–Simons theory on an oriented Lagrangian 3-submanifold M of a 6-manifold "X" arises as the string field theory of open strings ending on a D-brane wrapping "X" in the A-model topological string theory on "X". The B-model topological open string field theory on the spacefilling worldvolume of a stack of D5-branes is a 6-dimensional variant of Chern–Simons theory known as holomorphic Chern–Simons theory.