Flavour anomalies meet flavour symmetry

TL;DR

This paper proposes a Standard Model extension with a scalar leptoquark and a discrete flavour symmetry to explain B meson decay anomalies and the muon g-2, while satisfying experimental constraints.

Contribution

It introduces a novel flavour symmetry framework that suppresses unwanted leptoquark couplings, enabling simultaneous explanation of multiple flavour anomalies.

Findings

Successfully explains R(D) and R(D*) anomalies.

Accounts for muon anomalous magnetic moment.

Avoids experimental bounds from lepton flavour violation.

Abstract

We construct an extension of the Standard Model with a scalar leptoquark $\phi \sim (3,1,-\tfrac13)$ 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 $Z_{17}^{\rm diag}$, 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.