Doubly-charged scalar in four-body decays of neutral flavored mesons

Abstract：

We study the four-body decays of neutral flavored mesons, including $\bar K^0$, $D^0$, $\bar B^0$, and $\bar B_s^0$. These processes, which could be induced by a hypothetical doubly-charged scalar particle, do not conserve the lepton number. Assuming, as an example, that the mass of the doubly-charged particle is 1000 GeV, and using the upper bounds of the couplings, we calculate the branching ratios of different channels. For $\bar K^0\rightarrow h_1^+h_2^+e^-e^-$, $D^0\rightarrow h_1^-h_2^-e^+e^+$, and $\bar B_{d,s}^0\rightarrow h_1^+h_2^+e^-e^-$, it is of the order of $10^{-30}$, $10^{-32}$--$10^{-29}$, and $10^{-33}$--$10^{-28}$, respectively. Based on the experimental results for the $D^0\rightarrow h_1^-h_2^-l_1^+l_2^+$ channels, we also find the upper limit for the quantity $\frac{s_\Delta h_{ij}}{M_\Delta^2}$.