Implications of high precision experiments and the CDF top quark candidates

We discuss the consequences of recent experimental results from CDF, SLC, CERN LEP, and elsewhere for the standard model and for new physics, A global fit to all indirect precision data yields mₜ=175±{}11_-19⁺¹⁷ GeV, sin²{θ}^MS{}=0.2317(3)(2), and αₛ=0.127(5)(2), where the central values are for MH=300 GeV and the second uncertainties are for MH{→}1000 GeV (+) and 60 GeV (-). The mₜ value is in remarkable agreement with the value mₜ value is in remarkable agreement with the value mₜ=174±{}16 GeV suggested by the CDF candidate events. There is a slight preference for a light Higgs boson with MH730 (880) GeV at 95% C.L. if the CDF mₜ value is (not) included. The sensitivity is, however, due almost entirely to the anomalously large observed values for the Z{→}bb{} width and left-right asymmetry. The value of αₛ (from the line shape) is clean theoretically assuming the standard model, but is sensitive to the presence of new physics contributions to the Z{→}bb{} vertex. Allowing a vertex correction δbbⁿᵉʷ one obtains the significantly lower value αₛ=0.111±{}0.009, in better agreement with low energy determinations, and δbbⁿᵉʷ=0.023±{}0.011.There is now enough data to perform more general fits to parameters describing new physics effects and to separate these from mₜ and MH. Allowing the parameter ρ₀, which describes sources of SU(2) breaking beyond the standard model, to be free one finds ρ₀=1.0012±{}0.0017±{}0.0017, remarkably close to unity. One can also separate the new physics contributions to the oblique parameters Snew, Tnew, and Unew, which all take values consistent with zero. The effects of supersymmetry on the determination of the standard model parameters are discussed.