Minimal Vectorlike Leptonic Dark Matter And Signatures At The Lhc

We propose a minimal vectorlike leptonic dark matter (DM) with renormalizable interaction in a beyond-the-Standard- Model (SM) scenario, in which the SM is augmented with a vectorlike doublet and a singlet lepton. The additional fermions are odd under a discrete Z(2) symmetry, while the rest of the SM particles are singlets, thus providing stability to the DM. In this scenario, we show that the DM emerges as an admixture of the neutral component of the vectorlike doublet and the singlet leptons. The singlet-doublet mixing (sin theta) plays a crucial role in yielding the correct relic density as well as in obtaining null direct DM search results through an interplay of interactions via Z and Higgs mediation. The mixing is also strongly constrained from the invisible Z and Higgs decay width. We found that the correct relic abundance of DM can be obtained in a large region of parameter space for a DM mass larger than M-Z/2 and sin theta less than or similar to 0.1. The details of model phenomenology with collider signatures at the Large Hadron Collider (LHC) are discussed. In particular, we show that for sin theta less than or similar to 0.01, the charged companion of the DM can give rise to an observable displaced vertex signature, marking a significant departure from other fermionic DM scenarios, while keeping the relic abundance intact.