  The instability of dark matter may produce visible signals in the spectrum of
cosmic gamma-rays. We consider this possibility in frameworks with additional
spatial dimensions and supersymmetry. Examples of particles include
superweakly-interacting massive particles such as gravitinos in supersymmetry
models, the lightest Kaluza-Klein (KK) state in models with universal extra
dimensions, and weakly-interacting massive particles such as branons in
flexible brane-worlds.
