Constraints on dark matter annihilation and decay from the isotropic gamma-ray background

We study the constraints on dark matter (DM) annihilation/decay from the Fermi-LAT Isotropic Gamma-Ray Background (IGRB) observation. We consider the contributions from both extragalactic and galactic DM components. For DM annihilation, the evolution of extragalactic DM halos is taken into account. We find that the IGRB annihilation constraints under some DM subhalo models can be comparable to those derived from the observations of dwarf spheroidal galaxies and CMB. We also use the IGRB results to constrain the parameter regions accounting for the latest AMS-02 electron-positron anomaly. We find that the majority of DM annihilation/decay channels are strongly disfavored by the latest Fermi-LAT IGRB observation; only DM decays to μ⁺μ^- and 4μ channels may be valid. (authors)