Cosmic Gamma-ray from Inverse Compton Process in Unstable Dark Matter Scenario

Motivated by the PAMELA anomaly in the fluxes of cosmic-ray e+ and e-, we study the cosmic γ-ray induced by the inverse Compton (IC) scattering process in unstable dark matter scenario assuming that the anomaly is due to the e± emission by the decay of dark matter. We calculate the fluxes of IC-induced γ-ray produced in our Galaxy and that from cosmological distance, and show that both of them are significant. We discuss a possibility that large dark matter mass over TeV scale might be constrained by the γ-ray observation by Fermi Gamma-ray Space Telescope.