# Flavoured $B-L$ Local Symmetry and Anomalous Rare $B$ Decays

## TL;DR

This paper explores a flavoured $B-L$ gauge symmetry affecting third-generation fermions, proposing a low-energy model that can explain lepton universality violation hints at LHCb, while remaining consistent with neutrino masses and leptogenesis.

## Contribution

It introduces a novel flavoured $B-L$ gauge symmetry model with specific charge assignments, mechanisms for Yukawa coupling generation, and phenomenological implications including lepton universality violation.

## Key findings

- The new gauge boson can explain LHCb anomalies.
- The gauge coupling remains perturbative up to the Planck scale.
- Only two classes of vectorial $U(1)$ symmetries are consistent with leptogenesis.

## Abstract

We consider a flavoured $B-L$ gauge symmetry under which only the third generation fermions are charged. Such a symmetry can survive at low energies (~TeV) while still allowing for two superheavy right-handed neutrinos, consistent with neutrino masses via see-saw and leptogenesis. We describe a mechanism for generating Yukawa couplings in this model and also discuss the low-energy phenomenology. Interestingly, the new gauge boson could explain the recent hints of lepton universality violation at LHCb, with a gauge coupling that remains perturbative up to the Planck scale. Finally, we discuss more general $U(1)$ symmetries and show that there exist only two classes of vectorial $U(1)$ that are both consistent with leptogenesis and remain phenomenologically viable at low-energies.