Variational Quark Mass Expansion and the Order Parameters of Chiral Symmetry Breaking

We investigate in some details a ``variational mass" expansion approach, generalized from a similar construction developed in the Gross-Neveu (GN) model, to evaluate the basic order parameters of the dynamical breaking of the $SU(2)_L \times SU(2)_R$ and $SU(3)_L \times SU(3)_R$ chiral symmetries in QCD. The method starts with a reorganization of the ordinary perturbation theory with the addition of an {\em arbitrary} quark mass $m$. The new perturbative series can be summed to all orders thanks to renormalization group properties, with specific boudary conditions, and advocated analytic continuation in $m$ properties. In the approximation where the explicit breakdown of the chiral symmetries due to small current quark masses is neglected, we derive ansatzs for the dynamical contribution to the ``constituent" masses $M_q$ of the $u,d,s$ quarks; the pion decay constant $F_\pi$; and the quark condensate $\qq$ in terms of the basic QCD scale $\Lam $. Those ansatzs are then optimized, in a sense to be specified, and also explicit symmetry breaking mass terms can be consistently introduced in the framework. The values of $F_\pi$ and $M_q$ obtained are roughly in agreement with what is expected from other non-perturbative methods. In contrast we obtain quite a small value of $\vert latter results are briefly discussed.