Dynamical Chiral Symmetry Breaking from Variationally Improved Perturbative Expansion

We review how a specific resummation of the so-called “delta-expansion”, applied to the QCD Lagrangian, transforms the ordinary perturbative expansion in ${\alpha }_s$ into an expansion in an arbitrary mass parameter, around the basic scale $\bar{\mathrm{\Lambda }}$. When applied to the pole mass, the resulting expression may be interpreted as a dynamical mass ansatz, to be optimized with respect to the new expansion (mass) parameter. The construction is generalized to obtain estimates of the order parameters of the $SU(n_f{)}_L\times SU(n_f{)}_R$ ($n_f=2,3$) symmetry breakdown.