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Abstract
In this article we investigate in detail the possibility of accounting for the b → sℓ+ℓ− anomalies via box contributions involving with new scalars and fermions. For this purpose, we first write down the most general Lagrangian which can generate the desired effects and then calculate the generic expressions for all relevant b → s Wilson coefficients. Here we extend previous analysis by allowing that the new particles can also couple to right-handed Standard Model (SM) fermions as preferred by recent b → sℓ+ℓ− data and the anomalous magnetic moment of the muon.In the second part of this article we illustrate this generic approach for a UV complete model in which we supplement the Standard Model by a 4th generation of vector-like fermions and a real scalar field. This model allows one to coherently address the observed anomalies in b → sℓ+ℓ− transitions and in aμ without violating the bounds from other observables (in particular Bs − {overline{B}}_s mixing) or LHC searches. In fact, we find that our global fit to this model, after the recent experimental updates, is very good and prefers couplings to right-handed SM fermions, showing the importance of our generic setup and calculation performed in the first part of the article.
Highlights
While no particles beyond the ones of the Standard Model (SM) have been observed at the LHC, b → s + − data show a coherent pattern of deviations from the SM predictions with a significance of more than 4–5 σ [1,2,3,4,5,6,7,8]
In this article we investigate in detail the possibility of accounting for the b → s + − anomalies via box contributions involving with new scalars and fermions
Including these new measurements, global fits of the Wilson coefficients governing b → s + − transitions [12,13,14,15,16,17] still find that new physics (NP) scenarios can describe data much better than the SM, even though the preferences between the different scenarios changed with respect to the previous experimental situation
Summary
While no particles beyond the ones of the Standard Model (SM) have been observed at the LHC (so far), b → s + − data show a coherent pattern of deviations from the SM predictions with a significance of more than 4–5 σ [1,2,3,4,5,6,7,8]. Results of Belle and LHCb presented at Moriond EW 2019 [9, 10] confirmed these tensions, even though the significance for the new physics (NP) hypothesis, compared to the SM, did not change notably.1 Including these new measurements, global fits of the Wilson coefficients governing b → s + − transitions [12,13,14,15,16,17] still find that NP scenarios can describe data much better than the SM, even though the preferences between the different scenarios changed with respect to the previous experimental situation. [79] found that it is challenging to account for ∆aμ with TeV scale masses and not too large couplings to muons with a minimal particle content It has been argued [94] that one needs new sources of electroweak symmetry breaking (EWSB) if one aims at a high scale explanation of the anomalous magnetic moment of the muon.
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