Scalar Co-SIMP Dark Matter: Models and Sensitivities

TL;DR

This paper explores UV-complete models of Co-SIMP dark matter involving a unique 3-to-2 process with Standard Model particles, leading to light dark matter candidates that can be tested with upcoming low-threshold detectors.

Contribution

It introduces UV completions of the Co-SIMP mechanism with specific mediator couplings, highlighting the natural lightness of dark matter and potential experimental signatures.

Findings

Dark matter candidates are naturally light, sub-GeV or sub-MeV.

Late-time phase transitions expand viable parameter space.

Current and future experiments can probe these light dark matter models.

Abstract

In this work, we present UV completions of the recently proposed number-changing Co-SIMP freeze-out mechanism. In contrast to the standard cannibalistic-type dark matter picture that occurs entirely in the dark sector, the $3\to 2$ process setting the relic abundance in this case requires one Standard Model particle in the initial and final states. This prevents the dark sector from overheating and leads to rich experimental signatures. We generate the Co-SIMP interaction with a dark sector consisting of two scalars, with the mediator coupling to either nucleons or electrons. In either case, \textit{the dark matter candidate is naturally light}: nucleophilic interactions favor the sub-GeV mass range and leptophilic interactions favor the sub-MeV mass range. Viable thermal models in these lighter mass regimes are particularly intriguing to study at this time, as new developments in low-threshold detector technologies will begin probing this region of parameter space. While particles in the sub-MeV regime can potentially impact light element formation and CMB decoupling, we show that a late-time phase transition opens up large fractions of parameter space. These thermal light dark matter models can instead be tested with dedicated experiments. We discuss the viable parameter space in each scenario in light of the current sensitivity of various experimental probes and projected future reach.