  We investigate the spontaneous breaking of chiral symmetry in QCD by means of
a recently proposed approximation scheme in the Landau-gauge Curci-Ferrari
model, which combines an expansion in the Yang-Mills coupling and in the
inverse number of colors, without expanding in the quark-gluon coupling. The
expansion allows for a consistent treatment of ultraviolet tails via
renormalization group techniques. At leading order, it leads to the resummation
of rainbow diagrams for the quark propagator, with, however, a trivial running
of both the gluon mass and the quark-gluon coupling. In a previous work, by
using a simple model for a more realistic running of these parameters, we could
reproduce the known phenomenology of chiral symmetry breaking, including a
satisfactory description of the lattice data for the quark mass function. Here,
we get rid of this model-dependence by taking our approximation scheme to
next-to-leading order. This allows us to consistently include the realistic
running of the parameters and to access the unquenched gluon and ghost
propagators to first nontrivial order, which we can compare to available
lattice data for an even more stringent test of our approach. In particular,
our results for the various two-point functions compare well with lattice data
while the parameters of the model are strongly constrained.
