Regresar

Simultaneous explanation of R(D (∗)) and b→sμ + μ −: the last scalar leptoquarks standing

Abstract:

Over the past years, experiments accumulated intriguing hints for new physics (NP) in flavor observables, namely in the anomalous magnetic moment of the muon (aμ), in R(D(∗)) = Br(B → D(∗)τ ν)/Br(B → D(∗)ℓν) and in b → sμ+μ− transitions, which are all at the 3 − 4 σ level. In this article we point out that one can explain the R(D(∗)) anomaly using two scalar leptoquarks (LQs) with the same mass and coupling to fermions related via a discrete symmetry: an SU(2)L singlet and an SU(2)L triplet, both with hypercharge Y = −2/3. In this way, potentially dangerous contributions to b → sνν are avoided and non-CKM suppressed effects in R(D(∗)) can be generated. This allows for smaller overall couplings to fermions weakening the direct LHC bounds. In our model, R(D(∗)) is directly correlated to b → sτ+τ− transitions where an enhancement by orders of magnitude compared to the standard model (SM) is pbkp_redicted, such that these decay modes are in the reach of LHCb and BELLE II. Furthermore., one can also naturally explain the b → sμ+μ− anomalies (including R(K)) by a C9 = −C10 like contribution without spoiling μ − e universality in charged current decays. In this case sizable effects in b → sτ μ transitions are pbkp_redicted which are again well within the experimental reach. One can even address the longstanding anomaly in aμ, generating a sizable decay rate for τ → μγ. However, we find that out of the three anomalies R(D(∗)), b → sμ+μ− and aμ only two (but any two) can be explained simultaneously. We point out that a very similar phenomenology can be achieved using a vector leptoquark SU(2)L singlet with hypercharge 2/3. In this case, no tuning between couplings is necessary, but the model is non-renormalizable.