  We study the t-J-V model of a doped Mott insulator in connection to high-T_c
superconductors. The nearest neighbor Coulomb interaction (V) is treated
quantum mechanically on equal footing as the antiferromagnetic exchange
interaction (J). Motivated by the SU(2) symmetry at half-filling, we construct
a large-N theory which allows a systematic study of the interplay between
staggered flux order and superconductivity upon doping. We solve the model in
the large-N limit and obtain the ground state properties and the phase diagram
as a function of doping. We discuss the competition and the coexistence of the
staggered flux and the d-wave superconductivity in the underdoped regime and
the disappearance of superconductivity in the overdoped regime
