  Both regular (the zero-momentum ghost dressing function not diverging), also
named decoupling, and critical (diverging), also named scaling, Yang-Mills
propagators solutions can be obtained by analyzing the low-momentum behaviour
of the ghost propagator Dyson-Schwinger equation (DSE) in Landau gauge. The
asymptotic expression obtained for the regular or decoupling ghost dressing
function up to the order ${\cal O}(q^2)$ fits pretty well the low-momentum
ghost propagator obtained through the numerical integration of the coupled
gluon and ghost DSE in the PT-BFM scheme. Furthermore, when the size of the
coupling renormalized at some scale approaches some critical value, the PT-BFM
results seems to tend to the the scaling solution as a limiting case.
