Rare meson decay in supersymmetric theory with nonconservation of $R$-parity

The decay of mesons $K^{+}\to\pi^{-}\ell^{+}{\ell'}^{+}$ and $D^{+}\to K^{-}\ell^{+}{\ell'}^{+}$ ($\ell,\ell'=e,\mu$) involving a change of lepton number ${\Delta L=2}$ is considered in a supersymmetric extension of the standard model in which $R$-parity is not conserved due to trilinear Yukawa interactions. The obtained estimates for the probabilities of these decays are significantly lower than the direct experimental upper limits.