From the perspective of indirect detection, gamma rays would make excellent messengers of a potential dark matter signal. Not only do they point towards their sources, their energy spectrum may also carry smoking-gun features that allow to pinpoint the particle nature of dark matter. In particular, Bringmann et al. (2017) recently highlighted that excited Standard Model meson states, resulting from the annihilation or decay of GeV-scale dark matter candidates, give rise to distinctive MeV gamma-ray signatures.
Currently, there is a notable lack of experimental sensitivity in the MeV range. This has prompted several dedicated satellite mission proposals, like e-ASTROGAM, that would address the so-called 'MeV gap' within roughly a decade. Given the large astrophysical backgrounds, the presence of monochromatic lines or box shapes in the observed gamma-ray spectrum could be crucial in identifying a signal. Ongoing work focuses on how quarkonium resonances can further enhance such spectral features arising from transitions between heavy-meson states.