Gamma-rays From Warm WIMP Dark Matter Annihilation

The weakly interacting massive particle (WIMP) often serves as a candidate for the cold dark matter. However, when produced nonthermally, it could behave like warm dark matter. In this paper, we study the properties of the gamma-ray emission from annihilation of WIMP dark matter in the halo of our own Milky Way galaxy with high resolution N-body simulations of a Milky-Way-like dark matter halo, assuming a different nature of WIMPs. Due to the large free-streaming length in the scenario of warm WIMPs, the substructure content of the dark matter halo is significantly different from that of the cold WIMP counterpart, resulting in distinct predictions of the gamma-ray signals from the dark matter annihilation. We illustrate these by comparing the predicted gamma-ray signals from the warm WIMP annihilation to that of cold WIMPs. Pronounced differences from the subhalo sky map and statistical properties between two WIMP models are demonstrated. Due to the potentially enhanced cross section of the nonthermal production mechanism in the warm WIMP scenario, the Galactic center might be prior to the indirect detection of warm WIMPs to dwarf galaxies, which might be different from the cold dark matter scenario. As a specific example, we consider the nonthermally produced neutralino of the supersymmetric model and discuss the detectability of warm WIMPs with the Fermi gamma-ray telescope.