Quenched master field equations for unitary matrix models

We derive the quenched master field equations for constrained systems such as the O(N) non-linear sigma model. U(N)xU(N) chiral models, and U(N) lattice gauge theory. The master equations are algebraic, and involve quenching in both the space and ''fifth'' (Langevin) time directions. The quenched master field for the O(N) nonlinear sigma model is found exactly. The 0-dimensional unitary matrix model is solved perturbatively, and we recover the Gross-Witten result. The master equation for the U(N)xU(N) chiral model is set up for non-perturbative approximation methods, and some qualitative results are obtained. (orig.)