Bounds on mixing between light and heavy gauge bosons

Upper bounds are derived for the mixing between light and heavy gauge bosons in terms of the closeness of the observed $W$ or $Z$ mass to the SU(2)×U(1) prediction $m_0$. The mixing angles between light and heavy bosons with masses $m_1$ and $m_2$, respectively, are less than ${\left[\frac{({m_0}^2-{m_1}^2)}{({m_2}^2-{m_0}^2)}\right]}^{\frac{1}{2}}$. Existing data imply a limit of ≲ 0.04 for the mixing angle between the $W$ and a 1-TeV heavy boson. A similar result holds for the $Z$ if there are no Higgs multiplets with $I>\mathrm{}\frac{1}{2}$ with significant vacuum expectation values.