Limits on Flavor Changing Neutral Currents inD0Meson Decays

Using the CLEO II detector at the Cornell Electron Storage Ring, we have searched for flavor changing neutral currents and lepton family number violations in $D^0$ meson decays. The upper limits on the branching fractions for $D^0\to {\ell }^{+}{\ell }^{-}$ and $D^0\to X^0{\ell }^{+}{\ell }^{-}$ are in the range ${10}^{-5\mathrm{}}$ to ${10}^{-4\mathrm{}}$, where $X^0$ can be a ${\pi }^0$, $K_s^0$, $\eta$, ${\rho }^0$, $\omega$, ${\overline{K}}^{*0\mathrm{}}$, or $\phi$ meson, and the ${\ell }^{+}{\ell }^{-}$ pair can be $e^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{-}$, or $e^{\pm }{\mu }^{\mp }$. Although these limits are above the theoretical predictions, most are new or an order of magnitude lower than previous limits.