Abstract
We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both B-physics anomalies, viz. {R}_{D^{left(*right)}}^{exp }>{R}_{D^{left(*right)}}^{mathrm{SM}} or/and {R}_{K^{left(*right)}}^{exp }>{R}_{K^{left(*right)}}^{mathrm{SM}} . To do so we combine the constraints arising both from the low-energy observables and from direct searches at the LHC. We find that none of the scalar leptoquarks of mass mLQ ≃ 1 TeV can alone accommodate the above mentioned anomalies. The only single leptoquark scenario which can provide a viable solution for mLQ ≃ 1÷2 TeV is a vector leptoquark, known as U1, which we re-examine in its minimal form (letting only left-handed couplings to have non-zero values). We find that the limits deduced from direct searches are complementary to the low-energy physics constraints. In particular, we find a rather stable lower bound on the lepton flavor violating b → sℓ1±ℓ2∓ modes, such as ℬ(B → Kμτ). Improving the experimental upper bound on ℬ(B → Kμτ) by two orders of magnitude could compromise the viability of the minimal U1 model as well.
Highlights
> RDSM(∗) the lowenergy observables and from direct searches at the LHC
Single LQ solutions to the B-physics anomalies, We find that none of the scalar LQs alone, with
To arrive to that conclusion we combined a number of constraints on the model parameters arising from the low-energy flavor physics observables with those coming from the direct searches at the LHC
Summary
Effective theories provide an efficient way to describe the low-energy physics processes in which the short-distance physics is encoded in the so called Wilson coefficients, which. In order to describe the anomalies observed in the exclusive b → c νdecays one necessarily needs to introduce the new bosonic fields above the electroweak scale Such an extended theory should respect the SU(2)L × U(1)Y symmetry which means that gVR should be lepton flavor universal. We are left with four effective coefficients, gVL, gSL, gSR and gT which can potentially contribute to RD(∗). From which we derive that gP (mb) ≡ gSR (mb) − gSL(mb) ∈ (−1.14, 0.68) By combining this constraint with the low-energy fit to RD(∗) described above, we conclude in figure 2 that the scenario with gVL > 0 can accommodate RD(∗), and other scenarios such as gT (mb) = 0, gSL = −4 gT > 0.
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