We study the $D-\bar D$ mixing and rare D decays in the Littlest Higgs model. As the new weak singlet quark with the electric charge of 2/3 is introduced to cancel the quadratic divergence induced by the top-quark, the standard unitary $3\times 3$ Cabibbo-Kobayashi-Maskawa matrix is extended to a non-unitary $4\times 3$ matrix in the quark charged currents and Z-mediated flavor changing neutral currents are generated at tree level. In this model, we show that the $D-\bar D$ mixing parameter can be as large as the current experimental value and the decay branching ratio (BR) of $D\to X_u \ga$ is small but its direct CP asymmetry could be $O(10%)$. In addition, we find that the BRs of $D\to X_u \ell^{ +} \ell^{ -}$, $D\to X_u\nu \bar \nu$ and $D\to \mu^{ +} \mu^{ -}$ could be enhanced to be $O(10^{ -9})$, $O(10^{ -8})$ and $O(10^{ -9})$, respectively.
Categories: hep-ph hep-ex