EDGES of the Dark Forest

We propose a new method to hunt for dark matter using dark forest/absorption features across the full electromagnetic spectrum, especially in the bands where there is a desert i.e. regions where no strong lines from baryons are expected. Such unique signatures can arise for dark matter models with a composite nature and internal electromagnetic transitions. In the presence of a background source, such as a quasar, such interactions in the dark matter halos can produce a series of closely spaced absorption lines, which we call the dark forest. The dark forest feature is a sensitive probe of the dark matter self-interactions and the halo mass function, especially at the low mass end. Moreover, the absorption of CMB photons by dark matter gives rise to a global absorption signal in the CMB spectrum which can explain the anomalous absorption feature detected by the EDGES collaboration.