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

Motivated by the PAMELA anomaly in the fluxes of cosmic-ray e{sup +} and e{sup -}, we study the cosmic gamma-ray induced by the inverse Compton (IC) scattering process in unstable dark matter scenario assuming that the anomaly is due to the e{sup +}- emission by the decay of dark matter. We calculate the fluxes of IC-induced gamma-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 gamma-ray observation by Fermi Gamma-ray Space Telescope.