Data in B-meson decays indicate violations of lepton flavour universality, thereby raising the question about such phenomena in the charm sector. We perform a modelindependent analysis of NP contributions in (semi)-leptonic decays of D (s) mesons which originate from c → d¯ ν l and c → s¯ ν charged-current interactions. Starting from the most general low-energy effective Hamiltonian containing four-fermion operators and the corresponding shortdistance coefficients, we explore the impact of new

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... pseudo)scalar, vector and tensor operators and constrain their effects through the interplay with current data. We pay special attention to the elements |V cd | and |V cs | of the Cabibbo-Kobayashi-Maskawa matrix and extract them from the D (s) decays in the presence of possible NP decay contributions, comparing them with determinations utilizing unitarity. We find a picture in agreement with the Standard Model within the current uncertainties. Using the results from our analysis, we make also predictions for leptonic D + (s) → e + ν e modes which could be hugely enhanced with respect to their tiny Standard Model branching ratios. It will be interesting to apply our strategy at the future high-precision frontier. Eur. Phys. J. C (2020) 80:153 < R SM K and R exp K * < R SM K * . JHEP 08, 104 (2017). arXiv:1704.05835 [hep-ph]