Search for Higgs portal DM at the ILC

TL;DR

This paper investigates Higgs portal dark matter models at the ILC, focusing on how collider signatures can reveal the DM's spin and distinguish these models from effective theories, emphasizing the importance of model consistency.

Contribution

It introduces a detailed analysis of Higgs portal DM models at the ILC, highlighting the role of scalar mediator interference and the potential to determine DM spin through recoil-mass distributions.

Findings

Interference patterns in mono-Z signatures are significant for fermion and vector DM.

Shape analysis of recoil-mass distribution can identify DM spin.

Model consistency with renormalizability and unitarity is crucial for combining collider and direct detection results.

Abstract

Higgs portal dark matter (DM) models are simple interesting and viable DM models. There are three types of the models depending on the DM spin: scalar, fermion and vector DM models. In this paper, we consider renormalizable, unitary and gauge invariant Higgs portal DM models, and study how large parameter regions can be surveyed at the International Linear Collider (ILC) experiment at $\sqrt{s}=500$ GeV. For the Higgs portal singlet fermion and vector DM cases, the force mediator involves two scalar propagators, the SM-like Higgs boson and the dark Higgs boson. We show that their interference generates interesting and important patterns in the mono-$Z$ plus missing $E_T$ signatures at the ILC, and the results are completely different from those obtained from the Higgs portal DM models within the effective field theories. In addition, we show that it would be possible to distinguish the spin of DM in the Higgs portal scenarios, if the shape of the recoil-mass distribution is observed. We emphasize that the interplay between these collider observations and those in the direct detection experiments has to be performed in the model with renomalizability and unitarity to combine the model analyses in different scales.