How to save the WIMP: global analysis of a dark matter model with two s-channel mediators

TL;DR

This paper performs a comprehensive global analysis of a two-mediator dark matter model, considering various experimental constraints, and identifies the conditions under which thermal relic dark matter remains viable.

Contribution

It introduces a detailed global scan of the 2MDM model with two s-channel mediators, incorporating multiple experimental constraints to determine viable parameter regions.

Findings

Thermal DM is only viable near an s-channel resonance or if a mediator is lighter than DM.

Vector-mediated DM-nucleon scattering constrains the model despite velocity suppression.

Indirect detection is relevant when DM annihilates into both mediators kinematically.

Abstract

A reliable comparison of different dark matter (DM) searches requires models that satisfy certain consistency requirements like gauge invariance and perturbative unitarity. As a well-motivated example, we study two-mediator DM (2MDM). The model is based on a spontaneously broken $U(1)'$ gauge symmetry and contains a Majorana DM particle as well as two $s$-channel mediators, one vector (the $Z'$) and one scalar (the dark Higgs). We perform a global scan over the parameters of the model assuming that the DM relic density is obtained by thermal freeze-out in the early Universe and imposing a large set of constraints: direct and indirect DM searches, monojet, dijet and dilepton searches at colliders, Higgs observables, electroweak precision tests and perturbative unitarity. We conclude that thermal DM is only allowed either close to an $s$-channel resonance or if at least one mediator is lighter than the DM particle. In these cases a thermal DM abundance can be obtained although DM couplings to the Standard Model are tiny. Interestingly, we find that vector-mediated DM-nucleon scattering leads to relevant constraints despite the velocity-suppressed cross section, and that indirect detection can be important if DM annihilations into both mediators are kinematically allowed.