Twisting gauged non-linear sigma-models

We consider gauged sigma-models from a Riemann surface into a Kahler and hamiltonian G-manifold X. The supersymmetric N = 2 theory can always be twisted to produce a gauged A-model. This model localizes to the moduli space of solutions of the vortex equations and computes the Hamiltonian Gromov-Witten invariants. When the target is equivariantly Calabi-Yau, i.e. when its first G-equivariant Chern class vanishes, the supersymmetric theory can also be twisted into a gauged B-model. This model localizes to the Kahler quotient X//G.