Uncertainties from light quark loops

Abstract

The Standard Model has three input parameters (not counting fermion masses, higgs mass and mixings) that determine the couplings and masses of the vector bosons. Popular renormalization schemes use experimentally well measured quantities like the fine structure constant α = 1 / 137.0604(11) and the Fermi constant G_F = 1.166344(11)·10⁻⁵ GeV⁻² determined from the muon lifetime. The third parameter used to be sin²θ_w, determined from neutral-current processes. For LEP physics instead, will soon be measured to high precision and is therefore a good choice as third parameter. Using cosθ_w = M_W / M_Z as definition of the weak mixing angle, the tree level expression for M_W becomes M_W = A₀ / sinθ_w where ${{\text{A}}_0}\, = \,\sqrt {(\pi \alpha \,/\,\sqrt 2 {{\text{G}}_{\text{F}}})} \, = \,37.281$ GeV.