Dark Matter From Weak Polyplets

Abstract

The addition of new multiplets of fermions charged under the Standard Model gauge group is investigated, with the aim of identifying a possible dark matter candidate. These fermions are charged under $SU(2)\times U(1)$, and their quantum numbers are determined by requiring all new particles to obtain masses via Yukawa couplings and all triangle anomalies to cancel as in the Standard Model; more than one multiplet is required and we refer to such a set of these multiplets as a polyplet. For sufficiently large multiplets, the stability of the dark matter candidate is ensured by an accidental symmetry; for clarity, however, we introduce a model with a particularly simple polyplet structure and stabilize the dark matter by imposing a new discrete symmetry. We then explore the features of this model; constraints from colliders, electroweak precision measurements, the dark matter relic density, and direct detection experiments are considered. We find that the model can accommodate a viable dark matter candidate for large Higgs boson masses; for $m_H\sim 125$ GeV, a subdominant contribution to the dark matter relic density can be achieved.