Constraints on charged-Higgs-boson couplings

Using the experimental value of the $K_L-K_S$ mass difference, we derive constraints on charged-Higgs-boson couplings in gauge theories of the weak and electromagnetic interactions. These bounds severely restrict the possible magnitude of charged-Higgs-boson effects in $K$ and $D$ meson decays. Our results are based on the observation that charged-Higgs-boson-exchange contributions to $K^0-{\overline{K}}^0$ mixing are of order $\frac{1}{{M_H}^2}$ whereas the corresponding $W$-boson contribution is only of order $\frac{{m_c}^2}{{M_W}^4}$.