Non-perturbative results for level correlations from the replica nonlinear sigma model

We show that for all the three standard symmetry classes (unitary, orthogonal and symplectic), the conventional replica nonlinear sigma model gives the correct non-perturbative result for the two-level correlation functions R_2(\omega) of electrons in disordered metals in the limit of large \omega. In this limit, non-perturbative oscillatory contributions arise from a degenerate saddle-point manifold within this sigma model which corresponds to the replica-symmetry breaking. Moreover, we demonstrate that in the unitary case the very same results can be extracted from the well known exact integral representation for R_2(\omega).