Leptonic And Semileptonic D Decays And New Physics

In this thesis, on one hand, we investigated the decay rates of D meson decays from the basic computations of the Feynman diagrams in the Standard Model (SM). In this approach we derived analytically expressions for the square amplitudes of leptonic and semileptonic decays and finally used them to determine the analytic and numerical results for the decay rates. With the decay rates results at our disposal, we determined the branching ratios of leptonic and semileptonic decays separately within the SM.On the other hand, we focused on the effective Lagrangian (EL) under weak interaction from a general approach and used it in our calculation of differential decay rates of D mesons. Thereafter, we calculated the total decay rates via integration with respect to q2. In addition, using the total decay rates results, the branching ratios, q2 distributions and the contributions from the New Physics (NP) operators were investigated resulting in some phenomenologies of physics beyond the SM.Furthermore, we compared the results obtained within and beyond the SM as well as with the latest experimental data by drawing a compulsory analysis prior to our conclusion. We observed that the combination of experimental Cabbibo-Kobayashi-Maskawa (CKM) matrix measurements and theoretical decay constant calculations enabled the determination of the leptonic decay rate within the SM.