Fermi Constants and ``New Physics''

Abstract

Various precision determinations of the Fermi constant are compared. Included are muon and (leptonic) tau decays as well as indirect prescriptions employing $\alpha ,m_Z,m_W,\text{ssthwmzms},\Gamma (Z\to {\ell }^{+}{\ell }^{-})$, and $\Gamma (Z\to \nu \bar{\nu })$ as input. Their good agreement tests the standard model at the $\pm 0.1$ level and provides stringent constraints on new physics. That utility is illustrated for: heavy neutrino mixing, 2 Higgs doublet models, S, T, and U parameters and excited $W^{{\ast }^{\pm }}$ bosons (Kaluza-Klein excitations). For the last of those examples, $m_{W^{\ast }}\text{gsims}2.9$ TeV is found.

Comments: 14 pages