Lines and Boxes: Unmasking Dynamical Dark Matter through Correlations in
  the MeV Gamma-Ray Spectrum
  Identifying signatures of dark matter at indirect-detection experiments is
generally more challenging for scenarios involving non-minimal dark sectors
such as Dynamical Dark Matter (DDM) than for scenarios involving a single dark
particle. This additional difficulty arises because the partitioning of the
total dark-matter abundance across an ensemble of different constituent
particles with different masses tends to "smear" the injection spectra of
photons and other cosmic-ray particles that are produced via dark-matter
annihilation or decay. As a result, the imprints of the dark sector on these
cosmic-ray flux spectra typically take the form of continuum features rather
than sharp peaks or lines. In this paper, however, we identify an unambiguous
signature of non-minimal dark sectors such as DDM which can overcome these
issues and potentially be observed at gamma-ray telescopes operating in the MeV
range. We discuss the specific situations in which this signature can arise,
and demonstrate that this signature can be exploited in order to significantly
enhance our ability to resolve the unique spectral features of DDM and other
non-minimal dark sectors at future gamma-ray facilities.
