A 3d topological sigma model and D-branes

A 3d topological sigma model describing maps from a 3-manifold Y to a Calabi-Yau 3-fold M is introduced. As the model is topological, we can choose an arbitrary metric on M. Upon scaling up the metric, the path integral by construction localizes on the moduli space of special Lagrangian submanifolds of M. We couple the theory to dynamical gauge fields and discuss the case where M has a mirror and the gauge group is U(1).