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Recent experimental results on exclusive semi-tauonic B meson decays,B → D ( * ) τν, showing sizable deviations from the standard model prediction, suggest a new physics in which the structure of the relevant weak charged interaction may differ from that of the standard model. We study the exclusive semi-tauonic B decays in a model-independent manner using the most general set of four-Fermi interactions in order to clarify possible structures of the charged current in new physics. It turns out that correlations among observables including tau and D * polarizations and q 2 distributions are useful to distinguish possible new physics operators. Further, we investigate some interesting models to exhibit the advantage of our model-independent analysis. As a result, we find that two Higgs doublet models without tree-level flavor changing neutral currents (FCNC) and the minimal supersymmetric standard model with R-parity violation are unlikely to explain the present experimental data, while two Higgs doublet models with FCNC and a leptoquark model are consistent with the data.

R K and R D ( * ) are two B-decay measurements that presently exhibit discrepancies with the SM. Recently, using an effective field theory approach, it was demonstrated that a new-physics model can simultaneously explain both the R K and R D ( * ) puzzles. There are two UV completions that can give rise to the effective Lagrangian: (i) V B: a vector boson that transforms as an SU(2) L triplet, as in the SM, (ii) U 1 : an SU(2) L -singlet vector leptoquark. In this paper, we examine these models individually. A key point is that V B contributes to B 0 s -B 0 s mixing and τ → 3µ, while U 1 does not. We show that, when constraints from these processes are taken into account, the V B model is just barely viable. It predicts B(τ − → µ − µ + µ − ) 2.1 × 10 −8 . This is measurable at Belle II and LHCb, and therefore constitutes a smoking-gun signal of V B. For U 1 , there are several observables that may point to this model. Perhaps the most interesting is the lepton-flavor-violating decay Υ(3S) → µτ , which has previously been overlooked in the literature. U 1 predicts B(Υ(3S) → µτ )| max = 8.0 × 10 −7 . Thus, if a large value of B(Υ(3S) → µτ ) is observedand this should be measurable at Belle II -the U 1 model would be indicated.

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We study the longitudinal polarization of the tau lepton inB → Dτν decay. After discussing possible sensitivities of τ decay modes to the τ polarization, we examine the effect of charged Higgs boson on the τ polarization inB → Dτν. We find a relation between the decay rate and the τ polarization, and clarify the role of the τ polarization measurement in the search for the charged Higgs boson.

HEPfit is a flexible open-source tool which, given the Standard Model or any of its extensions, allows to (i) fit the model parameters to a given set of experimental observables; (ii) obtain predictions for observables. HEPfit can be used either in Monte Carlo mode, to perform a Bayesian Markov Chain Monte Carlo analysis of a given model, or as a library, to obtain predictions of observables for a given point in the parameter space of the model, allowing HEPfit to be used in any statistical framework. In the present version, around a thousand observables have been implemented in the Standard Model and in several new physics scenarios. In this paper, we describe the general structure of the code as well as models and observables implemented in the current release.

There are four models of tree-level new physics (NP) that can potentially simultaneously explain the b → sμ þ μ − and b → cτ −ν anomalies. They are the S 3 , U 3 and U 1 leptoquarks (LQs), and a triplet of standard-model-like vector bosons (VB's). Under the theoretical assumption that the NP couples predominantly to the third generation, previous analyses found that, when constraints from other processes are taken into account, the S 3 , U 3 and VB models cannot explain the B anomalies, but U 1 is viable. In this paper, we reanalyze these models, but without any assumption about their couplings. We find that, even in this most general case, S 3 and U 3 are excluded. For the U 1 model, constraints from the semileptonic leptonflavor-violating (LFV) processes B → K ðÃÞ μ AE τ ∓ , τ → μϕ and ϒ → μτ, which have been largely ignored previously, are found to be very important. Because of the LFV constraints, the pattern of couplings of the U 1 LQ is similar to that obtained with the above theoretical assumption. Also, the LFV constraints render unimportant those constraints obtained using the renormalization group equations. As for the VB model, it is excluded if the above theoretical assumption is made due to the additional constraints from B 0 s-B 0 s mixing, τ → 3μ and τ → μνν. By contrast, we find a different set of NP couplings that both explains the b → sμ þ μ − anomaly and is compatible with all constraints. However, it does not reproduce the measured values of the b → cτ −ν anomalies-it would be viable only if future measurements find that the central values of these anomalies are reduced. Even so, this VB model is excluded by the LHC bounds on highmass resonant dimuon pairs. This conclusion is reached without any assumptions about the NP couplings.