The SVZ-Expansion and Beyond

Abstract

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/ Q 2 -term (tachyonic gluon mass squared λ 2 ) 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 N c ) values, while the new 1/ Q 2 -term due to λ 2 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 ¯ s ( 2 GeV ) = ( 93 −32 +29 ) MeV and a more accurate value of the QCD coupling α s ( M Z ) = 0.117 ± 0.002 .