Dr Jean-Loic Kneur (LCC Montpellier)
A recent extension of a variationally optimized perturbation method, combined with renormalization group properties in a straightforward way, can provide a series of approximations to nonperturbative quantities such as the chiral symmetry breaking order parameters. We apply this to evaluate, up to the third order in this modified perturbation, the ratio F_\pi/\Lambda_MS where F_\pi is the pion decay constant and \Lambda_MS the basic QCD scale in the MS scheme. We also obtain from a similar approach the chiral quark condensate. We compare our estimates of \Lambda_MS and the chiral condensate with recent lattice calculation results.