Non-Standard Physics in Leptonic and Semileptonic Decays of Charmed Mesons

Recent measurements of the branching fraction for Ds → (ell)v disagree with the Standard Model expectation, which relies on calculations of fDs from lattice QCD. This paper uses recent preliminary measurements from CLEO and a new preliminary lattice-QCD result from this conference to update the significance of the discrepancy. The 'fDs puzzle' stands now at 3.5σ, with σ predominantly from the statistical uncertainty of the experiments. New physics scenarios that could solve the puzzle would also lead to non-Standard amplitudes mediating the semileptonic decays D → K(ell)v. This paper shows where the new amplitudes enter the differential rate and outlines where lattice QCD calculations are needed to confront recent and forthcoming measurements