Fluctuating topological invariants in string theory as an Abelian gauge   theory
  It is shown that the topological invariants associated with the two-dimensional world-surface in string theory have nontrivial fluctuations around their nonexistent classical dynamics. Additionally it is proved that the underlying geometrical structure in a covariant phase space formulation for such topological string actions mimics entirely that of an Abelian gauge theory 
R. Cartas-Fuentevilla