Cosmic Gamma-ray from Inverse Compton Process in Unstable Dark Matter
  Scenario
  Motivated by the PAMELA anomaly in the fluxes of cosmic-ray positron and
electron, 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 positron and electron 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.
