Minimal vectorlike leptonic dark matter and signatures at the LHC

Abstract

We propose a minimal vector-like leptonic dark matter (DM) with renormalisable interaction in a beyond the Standard Model (SM) scenario, where the SM is augmented with a vector-like doublet and a singlet leptons. The additional fermions are odd under a discrete Z2 symmetry, while the rest of the SM particles are singlets, and thus providing stability to the DM. In this scenario, we show that, the DM emerges as an admixture of the neutral component of the vector-like doublet and the singlet leptons. The singlet-doublet mixing (sin θ) 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 DM-mass larger than MZ /2 and sin θ < ∼ 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 θ < ∼ 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.

Singlet-doublet fermionic dark matter and gravitational waves in a two-Higgs-doublet extension of the Standard Model

“…The detailed study of collider signature for vector-like fermions can be found in [32,36,37,41]. As we have already seen, due to the presence of the second Higgs doublet large sin θ can be achieved satisfying both relic density and direct detection.…”

“…As a consequence, smaller mixing should give rise to smaller σ SI , making the DM parameter space more viable from direct search bound. The presence of the second Higgs helps in keeping the VLF mixing within a moderate limit, unlike the case in [32] where the bound on the mixing is even more stringent due to the presence of only one (SM) Higgs. This is a consequence of sin 2 α m 2 H suppression due to the heavier Higgs and small scalar mixing in case of scalar-mediated elastic scattering.…”

Radiative neutrino mass with ℤ 3 dark matter: from relic density to LHC signatures

“…In the most stringent case for a large mixing sin β ∼ 0.66, one gets |M N 2 −M N 1 | < 250 GeV. In the opposite case of a small mixing sin β < 0.1, |M N 2 − M E | is restricted to be less than a few GeV [39]. In our numerical analysis we will always work with a small β and assume N 2 , E are degenerate.…”

“…For light N 2 , the decays h → N 1N2 /N 2N1 , N 2N2 and Z → N 1N2 /N 2N1 , N 2N2 may also be allowed. These decay modes could provide more severe constraints [39], but are still weaker than the LUX constraint. Therefore we will not consider invisible decays as an individual constraint in our later analysis.…”

“…A brief discussion on such a signature with a much heavier N 1 at LHC has been performed in ref. [39].…”