The origin and nature of the dark matter in the Universe is one of the most pressing questions in fundamental physics. The combination of particle physics and cosmology has proven to be a successful avenue leading to the well-established theory of big bang nucleosynthesis that explains the primordial abundances of light elements. In the similar manner an extrapolation to even earlier times in the Universe has led to the WIMP (Weakly Interacting Massive Particle) freeze-out paradigm - one of the best motivated explanations of the dark matter relic abundance measured today. However, despite an enormous experimental effort no conclusive hint for WIMPs has been found, putting pressure on the WIMP dark matter explanation. In this talk we examine new avenues beyond the standard WIMP picture. We show that scrutinizing the well-known co-annihilation scenario and dropping the commonly made assumption of chemical equilibrium between co-annihilating partners offers new phenomenological possibilities. By solving the full coupled set of Boltzmann equations we find solutions that accommodate the measured dark matter density while requiring very small couplings that are in accordance with current null-results in WIMP searches. [continued below]
[cont.] Despite the very weak coupling the relic abundance is largely insensitive to the cosmological history prior to freeze-out, in contrast to other beyond-WIMP scenarios like freeze-in or superWIMPs. We discuss current constraints and motivate future searches. Furthermore, we examine the validity of kinetic equilibrium during freeze-out.