We present constraints on decaying and annihilating dark matter (DM) in the 4keV to 10 GeV mass range, using published results from the satellites HEAO-1,INTEGRAL, COMPTEL, EGRET, and the Fermi Gamma-ray Space Telescope. We deriveanalytic expressions for the gamma-ray spectra from various DM decay modes, andfind lifetime constraints in the range 10^24-10^28 sec, depending on the DMmass and decay mode. We map these constraints onto the parameter space for avariety of models, including a hidden photino that is part of a kineticallymixed hidden sector, a gravitino with R-parity violating decays, a sterileneutrino, DM with a dipole moment, and a dark pion. The indirect constraints onsterile-neutrino and hidden-photino DM are found to be more powerful than otherexperimental or astrophysical probes in some parts of parameter space. Whileour focus is on decaying DM, we also present constraints on DM annihilation toelectron-positron pairs. We find that if the annihilation is p-wave suppressed,the galactic diffuse constraints are, depending on the DM mass and velocity atrecombination, more powerful than the constraints from the Cosmic MicrowaveBackground.
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