  We analyse the phase diagram of the lattice gauged Nambu-Jona Lasinio model
with the help of a mean field approximation plus numerical simulations. We find
a phase transition line in the coupling parameters space separating the
chirally broken phase from the symmetric phase, which is in good qualitative
agreement with results obtained in the quenched-ladder approximation. The mean
field approximation relates the critical exponents along the continuous phase
transition line with the mass dependence of the chiral condensate in the
Coulomb phase of standard noncompact $QED$. Our numerical results for
noncompact $QED$ strongly suggest non mean field exponents along the critical
line.
