Updated standard model predictions for D (s) → P l + l − , l = e, µ, P = π, K and inclusive decays are presented. Model-independent constraints on |∆C| = |∆U | = 1 Wilson coefficients are worked out. New physics (NP) opportunities arise in semileptonic branching ratios for very large couplings only, however, are not excluded outside the resonance regions yet. The NP potential of resonanceassisted CP-asymmetries and angular observables is worked out. Predictions are given for leptoquark models, and include lepton flavor violating and dineutrino decays. Whether NP can be seen depends on flavor patterns, and vice versa.

The combined analysis of the BABAR, Belle, and LHCb data on B → Dτν, B → D à τν and B c → J=Ψτν decay observables shows evidence of physics beyond the Standard Model (SM). In this article, we study all the one-and two-dimensional scenarios which can be generated by adding a single new particle to the SM. We put special emphasis on the model-discriminating power of F L ðD Ã Þ and of the τ polarizations, and especially on the constraint from the branching fraction BRðB c → τνÞ. We critically review this constraint and do not support the aggressive limit of BRðB c → τνÞ < 10% used in some analyses. While the impact of F L ðD Ã Þ is currently still limited, the BRðB c → τνÞ constraint has a significant impact: depending on whether one uses a limit of 60%, 30% or 10%, the pull for new physics (NP) in scalar operators changes drastically. More specifically, for a conservative 60% limit a scenario with scalar operators gives the best fit to data, while for an aggressive 10% limit this scenario is strongly disfavored and the best fit is obtained in a scenario in which only a left-handed vector operator is generated. We find a sum rule for the branching ratios of B → Dτν, B → D à τν and Λ b → Λ c τν which holds for any NP contribution to the Wilson coefficients. This sum rule entails an enhancement of BRðΛ b → Λ c τνÞ over its SM prediction by ð24 AE 6Þ% for the current RðD ðÃÞ Þ data.

We present standard model (SM) estimates for exclusive c → uγ processes in heavy quark and hybrid frameworks. Measured branching ratios B(D 0 → (φ,K * 0 )γ) are at or somewhat exceeding the upper range of the SM and suggest slow convergence of the 1/m D , α s -expansion. Model-independent constraints on |∆C| = |∆U | = 1 dipole operators from B(D 0 → ρ 0 γ) data are obtained. Predictions and implications for leptoquark models are worked out. While branching ratios are SM-like CP asymmetries 10% can be induced. In SUSY deviations from the SM can be even larger with CP asymmetries of O(0.1). If Λ cbaryons are produced polarized, such as at the Z-pole, an angular asymmetry in Λ c → pγ decays can be studied that is sensitive to chirality-flipped contributions.

We systematically analyze the full angular distribution in D → P 1 P 2 l + l − decays, where P 1,2 = π, K, l = e, µ. We identify several null tests of the standard model (SM). Notably, the angular coefficients I 5,6,7 , driven by the leptons' axial-vector coupling C ( ) 10 , vanish by means of a superior GIM-cancellation and are protected by parity invariance below the weak scale. CP-odd observables related to the angular coefficients I 5,6,8,9 allow to measure CPasymmetries without D-tagging. The corresponding observables A 5,6,8,9 constitute null tests of the SM. Lepton universality in |∆c| = |∆u| = 1 transitions can be tested by comparing D → P 1 P 2 µ + µ − to D → P 1 P 2 e + e − decays. Data for P 1 P 2 = π + π − and K + K − on muon modes are available from LHCb and on electron modes from BESIII. Corresponding ratios of dimuon to dielectron branching fractions are at least about an order of magnitude away from probing the SM. In the future electron and muon measurements should be made available for the same cuts as corresponding ratios R D P1P2 provide null tests of e-µ-universality. We work out beyond-SM signals model-independently and in SM extensions with leptoquarks. I. INTRODUCTIONRare charm decays are notoriously challenging theoretically, yet offer singular insights into flavor in the up-quark sector [1]. With standard model (SM) branching ratios of |∆c| = |∆u| = 1 modes in the 10 −7 −10 −6 (semileptonic) and 10 −6 −10 −4 (radiative) range, precision studies are feasible at the experiments LHCb [2], Belle II [3] and BESIII [4]. In view of the substantial hadronic uncertainties there are three main avenues to probe for beyond the standard model (BSM) physics in charm: i) a measurement in an obvious excess of the SM such as the D → πµ + µ − branching ratio at high dilepton mass [5] -a window that can be closing soon [6], ii) extract the SM contribution from a SM-dominated mode and use SU (3) F , e.g., recently demonstrated for D → V γ, V = ρ,K * , φ and * Electronic address: stefan.boer@kit.edu † Electronic address: ghiller@physik.uni-dortmund.de arXiv:1805.08516v1 [hep-ph] 22 May 2018 ( ) 10 , and the suppression of CP, lepton flavor and lepton universality violation. Our proposal to test the SM with D → P 1 P 2 l + l − decays is based on these features, which allow to perform null tests and to identify new physics. An interpretation in terms