Toward (Finally!) Ruling Out Z and Higgs Mediated Dark Matter Models

TL;DR

This paper systematically evaluates Z and Higgs mediated WIMP dark matter models, finding most are already excluded by experiments, with only specific mass and coupling scenarios remaining viable, and predicting future experiments will test nearly all models.

Contribution

It provides a comprehensive, model-independent analysis of Z and Higgs mediated dark matter, identifying the remaining viable parameter space and guiding future experimental searches.

Findings

Most Z and Higgs mediated models are excluded by current data.

Viable models include specific mass ranges near resonance or above certain thresholds.

Future experiments will test nearly all remaining models.

Abstract

In recent years, direct detection, indirect detection, and collider experiments have placed increasingly stringent constraints on particle dark matter, exploring much of the parameter space associated with the WIMP paradigm. In this paper, we focus on the subset of WIMP models in which the dark matter annihilates in the early universe through couplings to either the Standard Model $Z$ or the Standard Model Higgs boson. Considering fermionic, scalar, and vector dark matter candidates within a model-independent context, we find that the overwhelming majority of these dark matter candidates are already ruled out by existing experiments. In the case of $Z$ mediated dark matter, the only scenarios that are not currently excluded are those in which the dark matter is a fermion with an axial coupling and with a mass either within a few GeV of the $Z$ resonance ($m_{\rm DM} \simeq m_Z/2$) or greater than 200 GeV, or with a vector coupling and with $m_{\rm DM} > 6$ TeV. Several Higgs mediated scenarios are currently viable if the mass of the dark matter is near the Higgs pole ($m_{\rm DM} \simeq m_H/2$). Otherwise, the only scenarios that are not excluded are those in which the dark matter is a scalar (vector) heavier than 400 GeV (1160 GeV) with a Higgs portal coupling, or a fermion with a pseudoscalar (CP violating) coupling to the Standard Model Higgs boson. With the exception of dark matter with a purely pseudoscalar coupling to the Higgs, it is anticipated that planned direct detection experiments will probe nearly the entire range of models considered in this study.