Gamma rays from warm WIMP dark matter annihilation

Abstract

The weakly interacting massive particle (WIMP) often serves as a candidate for the cold dark matter, however when produced non-thermally 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 different nature of WIMPs. Due to the large free-streaming length in the scenario of warm WIMPs, the substructure contend 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 skymap and statistical properties between two WIMP models are demonstrated. Due to the potentially enhanced cross section of the non-thermal production mechanism in warm WIMP scenario, the Galactic center might be prior for 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 non-thermally produced neutralino of supersymmetric model and discuss the detectability of warm WIMPs with Fermi $\gamma$-ray telescope.