  By using mutual flux-attaching singular gauge transformations, we derive an
effective action describing the zero temperature quantum phase transition from
d-wave superconductor to underdoped regime. In this effective action, quantum
fluctuation generated vortices couple to quasi-particles by a mutual
statistical interaction with statistical angle \theta, the vortices are also
interacting with each other by long range interactions due to charge
fluctuation. Neglecting the charge fluctuation, we find a fixed line
characterized by \theta and calculate the universal spinon, vortex and mutual
Hall drag conductivities which continuously depend on \theta. Implications for
double layer quantum Hall systems are given. When incorporating the charge
fluctuation, we emphasize the importance of keeping the periodicity of the
mutual CS term at \theta= \pm 1/2 to get the correct critical behaviors and
point out possible future directions. The connection with Z_{2} gauge theory is
discussed.
