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

In this paper, we study the four-body decay processes of neutral flavored mesons, including ${\bar{K}}^0$, $D^0$, ${\bar{B}}^0$, and ${\bar{B}}_s^0$. These processes, which induced by a hypothetical doubly-charged scalar particle, violate the lepton number. The quantity $Br\times\left(\frac{s_\Delta h_{ij}}{m_\Delta^2}\right)^{-2}$ofdifferentchannelsarecalculated,where$s_\Delta$,$h_{ij}$,and$M_\Delta$ are parameters related to the doubly-charged scalar. For ${\bar{K}}^0\to h_1^{+}{h}_2^{+}{l}_1^{-}{l}_2^{-}$, $D^0\to h_1^{-}{h}_2^{-}{l}_1^{+}{l}_2^{+}$, and $\bar B_{d,s}^0\rightarrow h_1^+h_2^+l_1^-l_2^-$,itisoftheorderof$10^{-13}\sim 10^{-11}$ ${\rm GeV^4}$,$10^{-17}\sim 10^{-10}$ $\mathrm{G}\mathrm{e}{\mathrm{V}}^4$, and ${10}^{-17}\sim {10}^{-10}$ $\mathrm{G}\mathrm{e}{\mathrm{V}}^4$, respectively. Based on the experimental results for the $D^0\to h_1^{-}{h}_2^{-}{l}_1^{+}{l}_2^{+}$ channels, we also set the upper limit for $\frac{s_{\mathrm{\Delta }}{h}_{ij}}{M_{\mathrm{\Delta }}^2}$.