Landau theory for a metal-insulator transition

The nonlinear {σ} model for disordered interacting electrons is studied in spatial dimensions d>4. The critical behavior at the metal-insulator transition is determined exactly, and found to be that of a standard Landau-Ginzburg-Wilson φ⁴ theory with the single-particle density of states as the order parameter. All static exponents have their mean-field values, and the dynamical exponent z=3. $partial n / partial mu--- is critical with an exponent of 1/2, and the electrical conductivity vanishes with an exponent s=1. The transition is qualitatively different from the one found in the same model in a 2+{ε} expansion.