Multipartite Dark Matter with Scalars, Fermions and signatures at LHC

TL;DR

This paper proposes a two-component dark matter model with scalar and fermion particles, exploring their interactions, relic density, and potential signatures at the LHC, while evading direct detection constraints.

Contribution

It introduces a novel multipartite dark matter framework with scalar and fermion components, stabilized by a discrete symmetry, and analyzes their collider signatures and relic density.

Findings

Two-component DM model consistent with relic density and direct detection bounds.

Potential LHC signatures through hadronically quiet dilepton events.

Large parameter space for DM-DM conversion processes.

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 ($\chi_1,\chi_2$) and a doublet ($N$). Stability of the two DM components is achieved by a discrete $\mathcal{Z}_2 \times {\mathcal{Z}^\prime}_2$ symmetry, under which the additional fields transform suitably. Fermion fields having same $\mathcal{Z}_2 \times {\mathcal{Z}^\prime}_2$ charge ($N,\chi_1$ 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 ($\chi_2$) 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.