Fermi constants and "new physics"

Various precision determinations of the Fermi constant are compared. Included are muon and (leptonic) tan decays as well as indirect prescriptions employing alpha, m(Z), m(W), sin(2) theta(W)(m(Z))(<(MS)over bar>), Gamma(Z-->l(+)l(-)), and Gamma(Z --><nu(nu)over bar>) as input. Their good agreement tests the standard model at the +/-0.1% level and provides stringent constraints on new physics. That utility is illustrated for heavy neutrino mixing, two-Higgs-doublet models, S, T, and U parameters, and excited W*+/- bosons (Kaluza-Klein excitations). For the last of those examples, m(W*)greater than or similar to 2.9 TeV is found. [S0556-2821(99)02319-X].