Abstract
We study the implications of single leptoquark extensions of the Standard Model (SM) under the assumption that their enhanced Yukawa sectors are invariant under global Abelian flavour symmetries already present in SM mass terms. Such symmetries, assumed to be the ‘residual’ subgroups of an ultra-violet flavour theory, have previously been considered in order to predict fermionic mixing angles. Here we focus instead on their effect on the novel flavour structures sourced by the leptoquark representations that address the present {R}_{K^{(star )}} anomalies in semileptonic rare B-decays. Combined with existing flavour data, the residual symmetries prove to be extremely constraining; we find that the (quark-lepton) leptoquark Yukawa couplings fall within mathcal {O}(10) highly predictive patterns, each with only a single free parameter, when ‘normal’ (SM-like) hierarchies are assumed. In addition, proton decay for the scalar SU(2) triplet representation is naturally avoided in the residual symmetry approach without relying on further model building. Our results indicate that a simultaneous explanation for the {R}_{K^{(star )}} anomalies and the flavour puzzle may be achieved in a simplified, model-independent formalism.
Highlights
Present data [1,2] hint at lepton non-universality (LNU) and the breakdown of the Standard Model (SM) in the decay signatures of semileptonic rare B-decays
We study the implications of single leptoquark extensions of the Standard Model (SM) under the assumption that their enhanced Yukawa sectors are invariant under global Abelian flavour symmetries already present in SM mass terms
In this paper we explore the simultaneous explanation of RK ( ) with the flavour puzzle via an analysis of the global flavour symmetries of the SM Yukawa sector when enhanced by a single leptoquark field
Summary
Present data [1,2] hint at lepton non-universality (LNU) and the breakdown of the Standard Model (SM) in the decay signatures of semileptonic rare B-decays. Leptoquark extensions of the SM have been studied in light of Table 1 while considering the flavour problem before [13,18,27,28], albeit with different assumptions Outside of this enhanced field content, the core assumption of our study is that, regardless of the origins and structure of GF , its scale, or the mechanism associated to its breaking, it does so to the residual symmetries present in (6), and that these symmetries leave the new leptoquark Yukawa couplings invariant.
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