Co-annihilating dark matter: Effective operator analysis and collider phenomenology

Abstract

We study dark matter (DM) models in which there are two dark sector particles, χ1 and χ2, of near mass. In such models, co-annihilation of χ1 and χ2 may be the dominant process controlling the DM relic density during freeze-out in the early Universe. In this scenario, there is no significant contribution to direct and indirect detection signals, unless there exists an extreme degeneracy in the masses of the lightest dark sector particles. Therefore, relic density constraints and collider searches provide the most relevant information about these models. We consider Dirac fermion dark matter which couples to standard model (SM) particles via an effective operator. For the collider phenomenolo..