The last Complex WIMPs standing

TL;DR

This paper investigates complex electroweak multiplets as dark matter candidates, calculating their masses, exploring detection prospects at future colliders and experiments, and assessing constraints from precision measurements.

Contribution

It provides the first comprehensive calculation of WIMP masses for all allowed multiplets and analyzes their detectability at future experiments and colliders.

Findings

Most multiplets can be probed by future direct detection experiments.

A future muon collider can explore the entire parameter space of complex doublets.

Some WIMP regions evade direct detection but can be constrained by collider searches.

Abstract

We continue the study of weakly interacting massive particles (WIMP) started in [arXiv:2107.09688], focusing on a single complex electroweak $n$-plet with non-zero hypercharge added to the Standard Model. The minimal splitting between the Dark Matter and its electroweak neutral partner required to circumvent direct detection constraints allows only multiplets with hypercharge smaller or equal to 1. We compute for the first time all the calculable WIMP masses up to the largest multiplet allowed by perturbative unitarity. For the minimal allowed splitting, most of these multiplets can be fully probed at future large-exposure direct detection experiments, with the notable exception of the doublet with hypercharge 1/2. We show how a future muon collider can fully explore the parameter space of the complex doublet combining missing mass, displaced track and long-lived track searches. In the same spirit, we study how a future muon collider can probe the parameter space of complex WIMPs in regions where the direct detection cross section drops below the neutrino floor. Finally, we comment on how precision observables can provide additional constraints on complex WIMPs.