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. If the γ-ray flux is precisely determined by Fermi Gamma-ray Space Telescope for various line-of-sight directions, it will provide an important test of the decaying dark matter scenario.