Lepton non-universality in $B$ decays and fermion mass structure

TL;DR

This paper proposes models where new vector-like fermions and scalars explain B decay anomalies through radiative corrections, linking these anomalies to fermion mass structures and dark matter, while satisfying experimental constraints.

Contribution

The authors introduce two simple models with Abelian family symmetry that connect B anomalies, fermion masses, and dark matter, incorporating new vector-like fermions and scalars.

Findings

B anomalies can be explained by box diagrams with heavy quarks and lighter leptons.

Models are consistent with flavor mixing and experimental bounds.

Potential dark matter candidates among new states.

Abstract

We consider the possibility that the neutral-current $B$ anomalies are due to radiative corrections generated by Yukawa interactions of quarks and leptons with new vector-like quark and lepton electroweak doublets and new Standard Model singlet scalars. We show that the restricted interactions needed can result from an underlying Abelian family symmetry and that the same symmetry can give rise to an acceptable pattern of quark and charged lepton masses and mixings, providing a bridge between the non-universality observed in the B-sector and that of the fermion mass matrices. We construct two simple models, one with a single singlet scalar in which the flavour changing comes from quark and lepton mixing and one with an additional scalar in which the flavour changing can come from both fermion and scalar mixing. We show that for the case the new quarks are much heavier than the new leptons and scalars the $B$ anomalies can be due to box diagrams with couplings in the perturbative regime consistent with the bounds coming from $B_s- \bar B_s$, $K- \bar K$ and $D- \bar D$ mixing as well as other lepton family number violating processes. The new states can be dark matter candidates and, in the two scalar model with a light scalar of O(60) GeV and vector-like lepton of O(100) GeV, there can be a simultaneous explanation of the B-anomalies, the muon anomalous magnetic moment and the dark matter abundance.