  Based on an improved SU(2) slave-boson approach to the t-J Hamiltonian, we
derive a phase diagram of high $T_c$ cuprates which displays both the
superconducting and pseudogap phases in the plane of temperature vs. hole
doping rate. It is shown that the inclusion of phase fluctuations in the order
parameters results in a closer agreement with the observed superconducting
temperature(bose condensation line) of an arch shape as a function of hole
doping rate.
