The self-annihilation of dark matter particles with mass in the MeV range canproduce gamma rays via prompt or secondary radiation. The annihilation rate forsuch light dark matter particles is however tightly constrained by cosmicmicrowave background (CMB) data. Here we explore the possibility of discoveringMeV dark matter annihilation with future MeV gamma-ray telescopes taking intoaccount the latest and future CMB constraints. We study the optimal energywindow as a function of the dominant annihilation final state. We consider boththe (conservative) case of the dwarf spheroidal galaxy Draco and the (moreoptimistic) case of the Galactic center. We find that for certain channels,including those with one or two monochromatic photon(s) and one or two neutralpion(s), a detectable gamma-ray signal is possible for both targets underconsideration, and compatible with CMB constraints. For other annihilationchannels, however, including all leptonic annihilation channels and two chargedpions, CMB data rule out any significant signal of dark matter annihilation atfuture MeV gamma-ray telescopes from dwarf galaxies, but possibly not for theGalactic center.
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