Search for New Physics in Rare D Decays
  In many extensions of the standard model an additional up-like heavy quark appears. Its appearance induces flavour changing neutral current transition in the up-quark region at the tree level. We investigate possible effects of these models in the c->u l+ l- transitions. First we determine impact of new physics on the relevant Wilson coefficients and then we reevaluate the standard model long-distance contributions. We calculate differential branching ratio for the D+ -> pi+ l+ l- and D0 -> rho0 l+ l- decays. Among all D decay modes these two are the simplest ones for the experimental studies. We also determine the forward-backward asymmetry for the D0 -> rho0 l+ l- decay and we comment on the effects of the Littlest Higgs model in both decay modes. 
Svjetlana Fajfer and Sasa Prelovsek