Mass singularities in light quark correlators: The strange quark case

The correlators of light-quark currents contain mass singularities of the form ln(${\mathit{m}}^2$/${\mathit{Q}}^2$). It has been known for quite some time that these mass logarithms can be absorbed into the vacuum expectation values of other operators of appropriate dimension, provided that schemes without normal ordering are used. We discuss in detail this procedure for the case of the mass logarithms ${\mathit{m}}^4$ln(${\mathit{m}}^2$/${\mathit{Q}}^2$), including also the mixing with the other dimension-4 operators to two-loop order. As an application we present an improved QCD sum rule determination of the strange-quark mass. We obtain m${\mathrm{¯}}_{\mathit{s}}$(1 GeV)=171±15 MeV.