Gamma-ray Constraints on Decaying Dark Matter and Implications for
  IceCube
  Utilizing the Fermi measurement of the gamma-ray spectrum toward the Galactic
Center, we derive some of the strongest constraints to date on the dark matter
(DM) lifetime in the mass range from hundreds of MeV to above an EeV. Our
profile-likelihood based analysis relies on 413 weeks of Fermi Pass 8 data from
200 MeV to 2 TeV, along with up-to-date models for diffuse gamma-ray emission
within the Milky Way. We model Galactic and extragalactic DM decay and include
contributions to the DM-induced gamma-ray flux resulting from both primary
emission and inverse-Compton scattering of primary electrons and positrons. For
the extragalactic flux, we also calculate the spectrum associated with cascades
of high-energy gamma-rays scattering off of the cosmic background radiation. We
argue that a decaying DM interpretation for the 10 TeV-1 PeV neutrino flux
observed by IceCube is disfavored by our constraints. Our results also
challenge a decaying DM explanation of the AMS-02 positron flux. We interpret
the results in terms of individual final states and in the context of
simplified scenarios such as a hidden-sector glueball model.
