Strange Quark Mass Determination From Sum Rules For Hadronic Tau-Decays

We discuss the ratio of hadronic to leptonic tau-decays, that can be expanded in an operator product expansion. The sensitivity to the strange mass is increased, if only the flavor-breaking difference of strange to non-strange currents is considered, which leaves us with terms that are at leading order proportional to m_s^2. In this sum rule the scalar channel exhibits a very bad convergence behavior in the perturbation series, that we control by replacing the scalar OPE with a phenomenological ansatz for the scalar and pseudoscalar spectral functions. The spectral ansatz is compared to the theoretical (OPE) expressions and we show that the results agree within the uncertainties and that the uncertainties of our ansatz are smaller than those of the theoretical expressions. This allows us to considerably reduce the uncertainties in comparison to previous m_s determinations from tau-decays. Our final results are m_s(2 GeV) = 117+-17 MeV for the unitarity fit of |V_us| and m_s(2 GeV) = 103+-17 MeV for the Leutwyler-Roos value of |V_us|.