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

By Andreas Crivellin, D. Müller, T. Ota. 2017

336 citations recorded by the source corpus.

A bstractOver 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 predicted, 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 predicted 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.

Subfields: Artificial Intelligence, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/987cbdcfc9ed9891727b4c02fa40d828ecc290a8

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Citations in the corpus

Opportunities in Flavour Physics at the HL-LHC and HE-LHC (2018, neutral): “A similar statement applies to an alternative model featuring two scalar leptoquarks, S1, S3 [955].”
Beyond the Standard Model Physics at the HL-LHC and HE-LHC (2018, methodology): “A similar statement applies to an alternative model featuring two scalar leptoquarks, S1, S3 [453], with the projected reach at CLIC and HL-LHC shown in Fig.”
What is the scale of new physics behind the B-flavour anomalies? (2017, background): “This can also be achieved in non-minimal scenarios with two leptoquarks via a proper cancellation [36].”
B-physics anomalies: a guide to combined explanations (2017, methodology): “However, the flavour structure postulated in [26] leads to large cancellations in b → sνν̄ and potential tuning also in b → u chargedcurrent transitions.”
Patterns of New Physics in b → sℓ+ℓ− transitions in the light of recent data (2017, background): “Concerning LQs, here a single representation (the scalar SU(2)L triplet or the vector SU(2)L singlet with Y = 2/3) can generate a C9µ = −C10µ like solution [56–62] and this pattern can also be obtained in models with loop contributions from three heavy new scalars and fermions [63–65].”