Constraints on the electroweak universal parameters and the top and Higgs masses from updated LEP / SLC data

A global analysis is performed using the latest data from LEP and SLC. Constraints on the electroweak universal parameters (S, T, U) and on the masses of the top quark and Higgs boson within the Standard Model (SM) are investigated. The uncertainties due to the QCD and QED effective couplings, α s (m Z) and ¯ α(m 2 Z), are examined in detail. Even though the mean value of S is increased to be consistent with zero, the naive Technicolor models are still disfavored due to its reduced error. Within the SM, we find the 90 %CL constraints; 133 GeV < m t < 190 GeV and 10 GeV < m H < 440 GeV for α s (m Z) = 0.116 and 1/ ¯ α(m 2 Z) = 128.72. The experimental constraints on the Zb L b L vertex form-factor, ¯ δ b (m 2 Z), play an important role in disfavoring the region of large m t (m t ∼ 200 GeV) and large m H (m H ∼ 1000 GeV). If m t is precisely known, the present electroweak data give a rather strict upper bound on the Higgs mass, m H < 140 (300) GeV at 95% CL, for m t = 160 (175) GeV and for the above α s (m Z) and ¯ α(m 2 Z).