  Non-linear sigma models that arise from the supersymmetric approach to
disordered electron systems contain a non-compact bosonic sector. We study the
model with target space H^2, the two-hyperboloid with isometry group SU(1,1),
and prove that in three dimensions moments of the fields are finite in the
thermodynamic limit. Thus the non-compact symmetry SU(1,1) is spontaneously
broken. The bound on moments is compatible with the presence of extended
states.
