A combined explanation of the $B$-meson decay anomalies with a single vector leptoquark

TL;DR

This paper proposes a model with a single vector leptoquark to explain recent anomalies in B-meson decays, showing how non-unitary couplings from heavy fermion mixings can address lepton flavor universality violations.

Contribution

It introduces a vector leptoquark model with non-unitary couplings from heavy fermion mixings to simultaneously explain $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies.

Findings

Non-unitary couplings can reconcile anomalies with flavor bounds.

Heavy fermion mixings induce effective couplings that explain lepton flavor universality violation.

Future experiments could probe large parts of the model's parameter space.

Abstract

Motivated by the recent experimental progress on the $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$ anomalies in $B$-decays, we consider an extension of the Standard Model by a single vector leptoquark field. We study how one can achieve the required lepton flavour non-universality, starting from a priori universal gauge couplings. While the unitary coupling flavour structure, induced by the mass misalignment of quarks and leptons after $SU(2)_L$ breaking, does not allow to comply with stringent bounds from lepton flavour violating processes, we find that effectively non-unitary couplings, due to mixings with heavy vector-like fermions, hold the key to simultaneously address the $R_{K^{(\ast)}}$ and $R_{D^{(\ast)}}$ anomalies. Furthermore, in the near future, the expected progress in the sensitivity on charged lepton flavour violating observables should allow to probe a large region of the preferred parameter space in this class of vector leptoquark models.