EDGES of the dark forest: A new absorption window into the composite dark matter and large scale structure

TL;DR

This paper introduces a novel method to detect composite dark matter through absorption features across the electromagnetic spectrum, revealing potential signals in the dark forest and CMB spectrum that surpass current detection capabilities.

Contribution

The study proposes the dark forest as a new observational signature for dark matter, linking it to internal electromagnetic transitions and demonstrating its sensitivity to dark matter properties.

Findings

Dark forest features can probe dark matter self-interactions.

Absorption of CMB photons by dark matter causes detectable spectral distortions.

Potential explanation for EDGES anomalous absorption feature.

Abstract

We propose a new method to hunt for dark matter using dark forest/absorption features across the whole electromagnetic spectrum from radio to gamma rays, especially in the bands where there is a desert i.e. regions where no strong lines from baryons are expected. Such novel signatures can arise for dark matter models with a composite nature and internal electromagnetic transitions. The photons from a background source can interact with the dark matter resulting in an absorption signal in the source spectrum. In the case of a compact 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. We show that 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. There is a large volume of parameter space where dark forest is more sensitive compared to the best current and proposed direct detection experiments. Moreover, the absorption of CMB photons by dark matter gives rise to a global absorption signal in the CMB spectrum. For dark matter transition energies in the range $2.5\times 10^{-4}$ eV$-$ $5\times 10^{3}$ eV, such absorption features result in spectral distortions of the CMB in the COBE/FIRAS band of 60-600 GHz. If the dark matter transition frequency is $\sim$156 GHz, we show that the absorption of CMB photons by dark matter can provide an explanation for the anomalous absorption feature detected by the EDGES collaboration in 50-100 MHz range.