Versal deformations and superpotentials for rational curves in smooth   threefolds
  The versal deformation space of a smooth rational curve in a smooth complex threefold is explicitly computed under certain hypotheses. Under an additional hypothesis, the versal deformation space is then shown to be the variety of critical points of a holomorphic function, the superpotential, as predicted by the consideration of D-branes in string theory. 
Sheldon Katz