Projected SO(5) models

we construct a class of projected SO(5) models where the Gutwiller constrai nt of no-double-occupancy is implemented exactly. We introduce the concept of projected SO(5) symmetry where all static correlation functions are exac tly SO(5) symmetric and discuss the signature of the projected SO(5) symmet ry in dynamical correlation functions. We show that this class of projected SO(5) models can give a realistic description of the global phase diagram of the high-T-c superconductors and account for many of their physical prop erties. [S0163-1829(99)12241-0].