Abstract
We re-examine recent determinations of power corrections from tau-decay andconfront the results with the existing ones from QCD spectral sum rules (QSSR).We conclude that contrary to the QSSR analysis, which lead to =(6.8+-1.3)10^{-2} GeV^4, tau-decay is not a good place for extracting thegluon condensate due to its extra alpha_s^2 coefficient which suppresses itscontribution in this process. Results from e^+e^- sum rules and tau-decay: rhoalpha_s^2= (4.5+-0.3)10^{-4}GeV^6, where rho=3.0+-0.2 confirm the deviationfrom the vacuum saturation estimate of the four-quark condensate."Non-standard"power corrections (direct instantons, duality violation and tachyonic gluonmass) beyond the SVZ-expansion, partially cancel out in the V+A hadronictau-decay channel, which gives at order alpha_s^4:alpha_s(M_tau)=0.3249(29)_{ex}(75)_{th} leading to als(M_Z)|_tau=0.1192(4)_{ex}(9)_{th},in remarkable agreement with (but more accurate than)alpha_s(M_Z)|_Z=0.1191(27)obtained at the same alpha_s^4 order from the Z-widthand the global fit of electroweak data. Finally, the role of the tachyonicgluon mass in the determinations of |V_{us}|from tau-decay and of m_s fromtau-decay, e^+e^- and (pseudo)scalar channels is emphasized.