SYMMETRY AND WARD IDENTITIES FOR DISORDERED ELECTRON SYSTEMS

We study the field theory approach to Anderson localization in the framework of closed time path Green's function (CTPGF). The theory is found to be invariant under an Sp(2) group. Ward identities related to this symmetry are derived. A non-linear σ model arises as a consequence of the dynamical symmetry breaking caused by the imaginary part of the retarded Green's function.