The SVZ-Expansion and Beyond

I discuss the standard SVZ-expansion of the QCD two-point correlators in terms of the QCD vacuum condensates and beyond it due to a new unflavoured 1/Q2-term (tachyonic gluon mass squared λ2) which modelizes the effects of uncalculated higher order perturbative terms. The approach is confronted with low-energy and lattice data. One can notice that, in the different examples studied here, high-dimension condensates are expected to deviate largely from their vacuum saturation (large Nc) values, while the new 1/Q2-term due to λ2 solves the hadronic mass scale hierarchy-puzzle encountered in the early SVZ-sum rule analysis and improves the low-energy phenomenology. From tau-decay data, one can extract the running strange quark mass m-bar s(2 GeV)=(93-32+29) MeV and a more accurate value of the QCD coupling αs(MZ)=0.117±0.002