Searching for decaying and annihilating dark matter with line intensity mapping

The purpose of line-intensity mapping (IM), an emerging tool for extragalactic astronomy and cosmology, is to measure the integrated emission along the line of sight from spectral lines emitted from galaxies and the intergalactic medium. The observed frequency of the line then provides a distance determination allowing the three-dimensional distribution of the emitters to be mapped. Here we discuss the possibility to use these measurements to seek monoenergetic photons from dark-matter decay or possibly annihilation. The photons from decays or annihilations (should such lines arise) will be correlated with the mass distribution, which can be determined from galaxy surveys, weak-lensing surveys, or the IM mapping experiments themselves. We discuss how to seek this cross-correlation and then estimate the sensitivity of various IM experiments in the dark-matter mass-lifetime parameter space. We find prospects for improvements of nine orders of magnitude in sensitivity to decaying/annihilating dark matter in the frequency bands targeted for IM experiments.