Searching for new physics in D0→μ+μ−, e+e−, μ±e∓ at BES and/or the super charm-tau factory

In contrast with B0-B?0, Bs-B?s mixing where the standard model (SM) contributions overwhelm that of the new physics beyond standard model (BSM), a measured relatively large D0-D?0 mixing where the SM contribution is negligible, definitely implies the existence of the new physics BSM. It is natural to consider that the rare decays of D meson might be more sensitive to new physics, and the decay mode D0??+?? could be an ideal area to search for new physics because it is a flavor changing process. In this work we look for a trace of the new physics BSM in the leptonic decays of D0. Concretely we discuss the contributions of unparticle or an extra gauge boson Z' while imposing the constraints set by fitting the D0-D?0 mixing data. We find that the long-distance SM effects for D0 ?ll? still exceed those contributions of the BSM under consideration, but for a double-flavor changing process such as D0???e, the new physics contribution would be significant.