Exact generating function of a zero-dimensional supersymmetric non-linear sigma model

We compute exactly the generating function of a supersymmetric non-linear sigma model describ-ing random matrices belonging to the unitary class. Although an arbitrary source explicitly breaksthe supersymmetry, a careful analysis of the invariance of the generating function allows us to showthat it depends on only three invariant functions of the source. This generating function allows usto recover various results found in the literature. It also questions the possibility of a functionalrenormalization group study of the three-dimensional Anderson transition.