Reconciling $B$-decay anomalies with neutrino masses, dark matter and constraints from flavour violation

TL;DR

This paper proposes a Standard Model extension with scalar leptoquarks and Majorana fermions to explain B-decay anomalies, generate neutrino masses, and provide a dark matter candidate, while satisfying various experimental constraints.

Contribution

It introduces a novel model with specific leptoquark and fermion content, linking B-decay anomalies, neutrino masses, and dark matter within a unified framework.

Findings

Successfully explains $R_{K^{(*)}}$ anomalies with certain flavor textures.

Identifies key experimental constraints from meson decays and lepton flavor violation.

Provides viable dark matter candidate compatible with collider searches.

Abstract

Motivated by an explanation of the $R_{K^{(*)}}$ anomalies, we propose a Standard Model extension via two scalar SU(2)$_L$ triplet leptoquarks and three generations of triplet Majorana fermions. The gauge group is reinforced by a $Z_2$ symmetry, ensuring the stability of the lightest $Z_2$-odd particle, which is a potentially viable dark matter candidate. Neutrino mass generation occurs radiatively (at the three-loop level), and leads to important constraints on the leptoquark couplings to leptons. We consider very generic textures for the flavour structure of the $h_1$ leptoquark Yukawa couplings, identifying classes of textures which succeed in saturating the $R_{K^{(*)}}$ anomalies. We subsequently carry a comprehensive analysis of the model's contributions to numerous high-intensity observables such as meson oscillations and decays, as well as charged lepton flavour violating processes, which put severe constraints on the flavour structure of these leptoquark extensions. Our findings suggest that the most constraining observables are $K^+ \to \pi^+ \nu \bar \nu$ decays, and charged lepton flavour violating $\mu -e$ conversion in nuclei (among others). Nevertheless, for several classes of flavour textures and for wide mass regimes of the new mediators (within collider reach), this Standard Model extension successfully addresses neutrino mass generation, explains the current $R_{K^{(*)}}$ tensions, and offers a viable dark matter candidate.