Multipartite dark matter with scalars, fermions and signatures at LHC

Abstract

Basic idea of this analysis is to achieve a two-component dark matter (DM) framework composed of a scalar and a fermion, with non-negligible DM-DM interaction contributing to thermal freeze out (hence relic density), but hiding them from direct detection bounds. We therefore augment the Standard Model (SM) with a scalar singlet (S) and three vectorlike fermions: two singlets (χ 1 , χ 2 ) and a doublet (N). Stability of the two DM components is achieved by a discrete Z2×Z2′ symmetry, under which the additional fields transform suitably. Fermion fields having same Z2×Z2′ charge (N, χ 1 in the model) mix after electroweak symmetry breaking (EWSB) and the lightest component becomes one of the DM candidates, while scalar singlet S is the other DM component connected to visible sector by Higgs portal coupling. The heavy fermion (χ 2 ) plays the role of mediator to connect the two DM candidates through Yukawa interaction. This opens up a large parameter space for the heavier DM component through DM-DM conversion. Hadronically quiet dilepton signature, arising from the fermion dark sector, can be observed at Large Hadron Collider (LHC) aided by the presence of a lighter scalar DM component, satisfying relic density and direct search bounds through DM-DM conversion.