Mitigating Direct Detection Bounds in Non-minimal Higgs Portal Scalar Dark Matter Models

Abstract

Minimal scalar Higgs portal dark matter model is increasingly in tension with recent results form direct detection experiments like LUX and XENON. In this paper we make a systematic study of minimal extension of the ${\mathbb{Z}}_2$ stabilised singlet scalar Higgs portal scenario in terms of their prospects at direct detection experiments. We consider both enlarging the stabilising symmetry to ${\mathbb{Z}}_3$ and incorporating multipartite features in the dark sector. We demonstrate that in these non-minimal models the interplay of annihilation, co-annihilation and semi-annihilation processes considerably relax constraints from present and proposed direct detection experiments while simultaneously saturating observed dark matter relic density. We explore in particular the resonant semi-annihilation channel within the multipartite ${\mathbb{Z}}_3$ framework which results in new unexplored regions of parameter space that would be difficult to constrain by direct detection experiments in the near future. The role of dark matter exchange processes within multi-component ${\mathbb{Z}}_3\times {\mathbb{Z}}_3^{\prime }$ framework is illustrated. We make quantitative estimates to elucidate the role of the various annihilation processes in the different allowed regions of parameter space of these models.

31 pages, 15 figures, added brief discussion on vaccum stability and unitarity; minor changes in the text; updated references; typos fixed; matches published version