A quantitative description of the transition to a quantum disordered p
hase in a doped antiferromagnet, is obtained for the long-wavelength l
imit of the spin-fermion model, which is given by the O(3) non-linear
a model, a free fermionic part and current-current interactions. By ch
oosing local spin quantization axes for the fermionic spinor we show t
hat the low-energy limit of the model is equivalent to a U(1) gauge th
eory, where both the bosonic and fermionic degrees of freedom are mini
mally coupled to a vector gauge field. Within a large-N expansion, the
strength of the gauge fields is found to be determined by the gap in
the spin-wave spectrum, which is dynamically generated. The explicit d
oping dependence of the spin-gap is determined as a function of the pa
rameters of the original model. As a consequence of the above, the gau
ge-fields mediate a long-range interaction among dopant holes and S-1/
2 magnetic excitations only in the quantum disordered phase. The possi
ble bound-states in this regime correspond to charge-spin separation a
nd pairing.