Dark matter annihilation signals from the Large Magellanic Cloud and its impact on the Milky Way

Abstract: We study the dark matter (DM) annihilation signals from the Large Magellanic Cloud (LMC) and the impact of the LMC on the DM annihilation signals from the Milky Way (MW) halo, using a MW-LMC analogue from the Auriga magneto-hydrodynamical simulations. We find that the gamma-ray signals from DM annihilation from the LMC rises above the MW foreground by a factor of greater than 100 for the s-wave velocity-independent annihilation model, as well as for the Sommerfeld, p-wave, and d-wave velocity-dependent models. We derive upper limits on the annihilation cross section of DM particles in the LMC using Fermi-LAT data for all velocity-dependent cross section models. Bounds for d-wave annihilation are more stringent by $\sim 4-6$ orders of magnitude relative to previous bounds from dwarf galaxies, and for p-wave emission our bounds are $\sim 2-3$ orders of magnitude more stringent. We also demonstrate that the impact of the LMC on the DM annihilation signals from the MW halo is greatest for the p-wave and d-wave models towards the outer MW halo, while the impact is minimal for Sommerfeld and s-wave models. The LMC boosts the DM density and velocity distribution in the outer MW halo, both by bringing in high-speed DM particles and by accelerating the DM particles of the MW, affecting the DM annihilation signals from the MW for the p-wave and d-wave models.