Flavour anomalies meet flavour symmetry

Abstract

We construct an extension of the Standard Model with a scalar leptoquark $\varphi \sim (3,1,-\frac{1}{3})$ and the discrete flavour symmetry $G_f=D_{17}\times Z_{17}$ to explain anomalies observed in charged-current semi-leptonic $B$ meson decays and in the muon anomalous magnetic moment, together with the charged fermion masses and quark mixing. The symmetry $Z_{17}^{\mathrm{diag}}$, contained in $G_f$, remains preserved by the leptoquark couplings, at leading order, and efficiently suppresses couplings of the leptoquark to the first generation of quarks and/or electrons, thus avoiding many stringent experimental bounds. The strongest constraints on the parameter space are imposed by the radiative charged lepton flavour violating decays $\tau \to \mu \gamma$ and $\mu \to e\gamma$. A detailed analytical and numerical study demonstrates the feasibility to simultaneously explain the data on the lepton flavour universality ratios $R(D)$ and $R(D^{\star })$ and the muon anomalous magnetic moment, while passing the experimental bounds from all other considered flavour observables.

71 pages + appendices, 27 figures Matches version accepted for publication in Physical Review D

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