Abstract
In thermal dark matter models, allowing the dark matter candidate to coannihilate with another particle can considerably loosen the relic density constraints on the dark matter mass. In particular, introducing a single strongly interacting coannihilation partner in a dark matter model can bring the upper bound on the dark sector energy scale from a few TeV up to about 10 TeV. While these energies are outside the LHC reach, a large part of the parameter space for such coannihilating models can be explored by future hadron colliders. In this context, it is essential to determine whether the current bounds on dark matter simplified models also hold in non-minimal scenarios. In this paper, we study extended models that include multiple coannihilation partners. We show that the relic density bounds on the dark matter mass in these scenarios are stronger than for the minimal models in most of the parameter space and that weakening these bounds requires sizable interactions between the different species of coannihilation partners. Furthermore, we discuss how these new interactions as well as the additional particles in the models can lead to stronger collider bounds, notably in jets plus missing transverse energy searches. This study serves as a vital ingredient towards the determination of the highest possible energy scale for thermal dark matter models.
Highlights
Dark matter to reach masses of up to 10 TeV without overclosing the Universe [6–16]
For coannihilating dark matter scenarios, using the simplified model formalism has allowed to translate results from the LHC searches into limits on the mass of the dark matter [90–98] and on its splitting with its coannihilation partner X
We evaluated the robustness of these simplified model results against introducing new coannihilation partners
Summary
We discuss how increasing the number of coannihilation partners affects the dark matter relic density. We derive the conditions under which adding new coannihilation partners significantly increases the dark matter annihilation rate. Since our goal is to determine how heavy the dark matter mass can be in thermal scenarios, we only consider strongly interacting coannihilation partners, that typically lead to the largest annihilation rates in the dark sector. We follow the approach described in [6], focusing on several representative models that allow to derive generic conclusions about strongly interacting coannihilating dark sectors. We describe the simplified models that we will use throughout this paper and present a few examples of how introducing additional coannihilation partners can affect the dark matter relic density constraints
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