Editor: M. Cvetič At present, there are several hints of lepton flavor non-universality. The LHCb Collaboration has measured. In all cases, the experimental results differ from the standard model predictions by 2-3σ . Recently, an explanation of the R K puzzle was proposed in which new physics (NP) generates a neutral-current operator involving only third-generation particles. Now, assuming the scale of NP is much larger than the weak scale, this NP operator must be made invariant under the full SU(3) C × SU(2) L × U (1) Y gauge group. In this Letter, we note that, when this is done, a new charged-current operator can appear, and this can explain the R(D ( * ) ) puzzle. A more precise measurement of the double ratio R(D)/R(D * ) can rule out this model. + −ν ) = 0.332 ± 0.024 ± 0.018,where = e, μ. The SM predictions are R(D) = 0.297 ± 0.017 and R(D * ) = 0.252 ± 0.003 [3,5], which deviate from the BaBar mea-* Corresponding author.

The recent measurement of RK * is yet another hint of new physics (NP), and supports the idea that it is present in b → sµ + µ − decays. We perform a combined model-independent and modeldependent analysis in order to deduce properties of this NP. Like others, we find that the NP must obey one of two scenarios:, is rejected largely because it predicts RK = 1, in disagreement with experiment. The simplest NP models involve the tree-level exchange of a leptoquark (LQ) or a Z boson. We show that scenario (II) can arise in LQ or Z models, but scenario (I) is only possible with a Z . Fits to Z models must take into account the additional constraints from B 0 s -B 0 s mixing and neutrino trident production. Although the LQs must be heavy, O(TeV), we find that the Z can be light, e.g., M Z = 10 GeV or 200 MeV.

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.