  A simple version of the Bardeen-Cooper-Schrieffer (BCS)-type mean-field
theory for the t-J model is developed. The present approach rigorously treats
the constraint of no doubly occupied states and invokes two local order
parameters to implement spontaneous breaking of the global U(1)\times U(1)
symmetry. This is achieved by identifying the Hubbard operators with generators
of the su(2|1) superalgebra in the fundamental representation and employing the
CP^{1|1} parameterization for dynamical variables. As a result, an improved
phase diagram T_c(\delta) in the paramagnetic phase is obtained.
