  We investigate a new class of dark matter: superweakly-interacting massive
particles (superWIMPs). As with conventional WIMPs, superWIMPs appear in
well-motivated particle theories with naturally the correct relic density. In
contrast to WIMPs, however, superWIMPs are impossible to detect in all
conventional dark matter searches. We consider the concrete examples of
gravitino and graviton cold dark matter in models with supersymmetry and
universal extra dimensions, respectively, and show that superWIMP dark matter
satisfies stringent constraints from Big Bang nucleosynthesis and the cosmic
microwave background.
