A Fermionic Portal to Vector Dark Matter from a New Gauge Sector

Abstract

We present a new class of Dark Matter (DM) models wherein the Standard Model (SM) is extended with a new $SU(2)_D$ dark gauge sector. In this framework the stability of DM is provided by the conservation of a $U(1)$ global symmetry, which upon appropriate charge assignments for the $SU(2)_D$ multiplets, effectively leads to a $\mathbb{Z}_2$ symmetry subgroup. The origin of the global $U(1)$ symmetry which ensures the stability of DM can be justified in the form of a dark EW sector or through an underlying composite structure. The key ingredient of the model is a Vector-Like (VL) fermion doublet of $SU(2)_D$ , the members of which are singlets of the SM Electro-Weak (EW) gauge group, which mediate the interactions between the dark sector and the SM, via new Yukawa interactions. This class of models, labelled as Fermion Portal Vector DM (FPVDM), allows multiple realisations, depending on the properties of the the VL partner and the scalar potential. After spontaneous breaking of the $SU(2)_D$ symmetry via a new scalar doublet, the ensuing massive vector bosons with non-zero dark-isospin are DM candidates. The new class of FPVDM models suggested here has numerous phenomenological implications for collider and non-collider studies. As a practical example, we discuss here in detail a realisation involving a VL top partner assuming no mixing between the two physical scalars of the theory, the SM Higgs boson and its counterpart in the dark sector. We thus provide bounds on this setup from both collider and astroparticle observables.