The thermal relic density of dark matter is conventionally set by two-body annihilations. We point out that in many simple models, 3 → 2 annihilations can play an important role in determining the relic density over a broad range of model parameters. This occurs when the two-body annihilation is kinematically forbidden, but the 3 → 2 process is allowed; we call this scenario not-forbidden dark matter . We illustrate this mechanism for a vector-portal dark matter model, showing that for a dark matter mass of m χ ～ MeV ? 10 ? ? GeV , 3 → 2 processes not only lead to the observed relic density, but also imply a self-interaction cross section that can solve the cusp/core problem. This can be accomplished while remaining consistent with stringent CMB constraints on light dark matter, and can potentially be discovered at future direct detection experiments.
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