Supersymmetry for Systems with Unitary Disorder: Circular Ensembles

A generalized Hubbard-Stratonovitch transformation relating an integral over random unitary N times N matrices to an integral over Efetov’s unitary sigma model manifold, is introduced. This transformation adapts the supersymmetry method to disordered and chaotic systems that are modeled not by a Hamiltonian but by their scattering matrix or time-evolution operator. In contrast to the standard method, no saddle-point approximation is made, and no massive modes have to be eliminated. This first paper on the subject applies the generalized Hubbard-Stratonovitch transformation to Dyson’s Circular Unitary Ensemble. It is shown how to use a supersymmetric variant of the Harish-Chandra-Itzykson-Zuber formula to compute, in the large-N limit, the n-level correlation function for any n. Nontrivial applications to random network models, quantum chaotic maps, and lattice gauge theory, are expected.