Indirect Detection of Dark Matter Absorption in the Galactic Center

We consider the nuclear absorption of dark matter as an alternative to thetypical indirect detection search channels of dark matter decay orannihilation. In this scenario, an atomic nucleus transitions to an excitedstate by absorbing a pseudoscalar dark matter particle and promptly emits aphoton as it transitions back to its ground state. The nuclear excitation ofcarbon and oxygen in the Galactic Center would produce a discrete photonspectrum in the 𝒪(10) MeV range that could be detected by gamma-raytelescopes. Using the large-scale shell-model code, wecalculate the excitation energies of carbon and oxygen. We constrain the darkmatter-nucleus coupling for current COMPTEL data, and provide projections forfuture experiments AMEGO-X, e-ASTROGAM, and GRAMS for dark matter masses from∼ 10 to 30 MeV. We find the excitation process to be very sensitive to thedark matter mass and find that the future experiments considered would improveconstraints on the dark matter-nucleus coupling within an order of magnitude.