Flavourful $Z'$ portal for vector-like neutrino Dark Matter and $R_{K^{(*)}}$

TL;DR

This paper proposes a flavourful $Z'$ portal model linking vector-like neutrino dark matter to flavour anomalies in B-decays, consistent with experimental constraints and explaining both dark matter relic abundance and $R_{K^{(*)}}$ measurements.

Contribution

It introduces a novel $Z'$ portal model that connects vector-like neutrino dark matter with flavour anomalies, incorporating mixing effects to explain experimental observations.

Findings

The model can simultaneously explain $R_{K^{(*)}}$ anomalies and dark matter relic abundance.

Parameter space is identified consistent with collider, direct, and indirect detection constraints.

The $Z'$ couples to the fourth family and acquires induced couplings to second and third families.

Abstract

We discuss a flavourful $Z'$ portal model with a coupling to fourth-family singlet Dirac neutrino dark matter. In the absence of mixing, the $Z'$ is fermiophobic, having no couplings to the three chiral families, but does couple to a fourth vector-like family. Due to mixing effects, the $Z'$ gets induced couplings to second family left-handed lepton doublets and third family left-handed quark doublets. This model can simultaneously account for the measured $B$-decay ratios $R_{K}$ and $R_{K^*}$ and for the observed relic abundance of dark matter. We identify the parameter space where this explanation is consistent with existing experimental constraints from dark matter direct and indirect detection, LHC searches, and precision measurements of flavour mixing and neutrino processes.