Simplified Models of Flavourful Leptoquarks

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.

29 pages. v2: new section on qualitative discussion of collider implications and some clarifying edits added. Matches published version

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• $R_2$ as a single leptoquark solution to $R_{D^{(\ast )}}$ and $R_{K^{(\ast )}}$
• Combined Constraints on First Generation Leptoquarks
• Scalar Leptoquarks in Leptonic Processes
• Effective Theory Approach to New Physics with Flavour: General Framework and a Leptoquark Example
• Unified explanation of flavor anomalies, radiative neutrino mass and ANITA anomalous events in a vector leptoquark model
• Combined Explanation of the $Z\to b\bar{b}$ Forward-Backward Asymmetry, the Cabibbo Angle Anomaly, $\tau \to \mu \nu \nu$ and $b\to s{\ell }^{+}{\ell }^{-}$ Data
• A Common Origin of Neutrino Masses and $R_{D^{(\ast )}}$, $R_{K^{(\ast )}}$ Anomalies
• Leptoquarks in Oblique Corrections and Higgs Signal Strength: Status and Prospects
• Complete Lagrangian and Set of Feynman Rules for Scalar Leptoquarks
• Constraining flavour patterns of scalar leptoquarks in the effective field theory
• New Physics in $b\to s\mu \mu$: FCC-hh or a Muon Collider?
• Sensitivity of Future Hadron Colliders to Leptoquark Pair Production in the Di-Muon Di-Jets Channel
• Towards excluding a light $Z^{\prime }$ explanation of $b\to s{\ell }^{+}{\ell }^{-}$
• Finite Family Groups for Fermionic and Leptoquark Mixing Patterns
• Marriage between neutrino mass and flavor anomalies
• Addendum to: Combined Constraints on First Generation Leptoquarks
• Next-to-Leading-Order QCD Matching for $\Delta F=2$ Processes in Scalar Leptoquark Models
• FCNC-free multi-Higgs-doublet models from broken family symmetries
• Reconstructing Effective Lagrangians Embedding Residual Family Symmetries
• Search for charged-lepton-flavour violating $\mu \tau qt$ interactions in top-quark production and decay in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector at the LHC
• Residual Symmetries and Scalar Multiplet Vacuum Alignment in Non-Abelian Flavour Models
• Flavour anomalies meet flavour symmetry
• Rare decay $t\to c\gamma \gamma$ via scalar leptoquark doublets
• Explaining the hints for lepton flavour universality violation with three $S_2$ leptoquark generations