Constraints on dark matter with future MeV gamma-ray telescopes

A number of new balloon or space-based $\gamma$-ray observatories have been proposed to close a "MeV gap" in sensitivity to $\gamma$ rays in the MeV-GeV energy band. One aspect of the science case for these instruments is their ability to constrain or discover decaying or annihilating dark matter. In this work, we forecast the sensitivity of these instruments for dark matter annihilation or decay for a range of possible Standard Model final states and compare to existing bounds.