Limits on the strength of a left-right-symmetric electroweak interaction

We have investigated the constraints imposed on left-right-symmetric theories of weak and electromagnetic interactions by the $K_L-K_S$ mass difference, including the additional restrictions on the top-quark mass and mixing angles coming from the $K_L\to {\mu }^{+}{\mu }^{-}$ decay rate, and emphasizing the sensitivity of the results to various model-dependent assumptions. In the manifestly left-right-symmetric electroweak theory it was found that values for $m_R$, the mass of the charged right-handed boson $W_R$, as low as 220 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ (the original estimate of Bég, Budny, Mohapatra, and Sirlin) cannot be ruled out. However, for a large class of plausible models the lower bound on the mass of $W_R$ was found to be considerably higher, but still within the range that experiments now in progress will be able to explore. The lower bound on $m_R$ was also found to be quite sensitive to the value assumed for the top-quark mass and to the model-dependent values of the hadronic matrix elements of the quark operators, as well as to certain model-dependent assumptions regarding the dispersive part of the $K_L\to {\mu }^{+}{\mu }^{-}$ amplitude. We present the lower bound on $m_R$ for a wide range of the relevant parameters, which includes two specific models: the MIT bag model and the vacuum-insertion approximation.