A quantitative description of the transition to a quantum disordered p
hase in a doped antiferromagnet is obtained for the long-wavelength li
mit of the spin-fermion model, which is given by the O(3) nonlinear si
gma model, a free fermionic part and current-current interactions as o
btained by Shraiman and Siggia for the t - J model. By choosing local
spin quantization axes for the fermions we show that the low-energy li
mit of the model is equivalent to a U(1) gauge theory, where both the
bosonic and fermionic degrees of freedom are coupled minimally to a ve
ctor gauge field. Within a large-N expansion, the strength of the gaug
e fields is found to be determined by the gap in the spin-wave spectru
m, which is dynamically generated. The explicit doping dependence of t
he spin-gap is determined as a function of the parameters of the origi
nal model. As a consequence of the above, the gauge-fields mediate a c
onfining interaction among dopant holes and S-1/2 magnetic excitations
only in the quantum disordered phase. The possible bound-states in th
is regime correspond to charge-spin separation and pairing.