Deciphering the Archaeological Record: Cosmological Imprints of
  Non-Minimal Dark Sectors
  Many proposals for physics beyond the Standard Model give rise to a dark
sector containing many degrees of freedom. In this work, we explore the
cosmological implications of the non-trivial dynamics which may arise within
such dark sectors, focusing on decay processes which take place entirely among
the dark constituents. First, we demonstrate that such decays can leave
dramatic imprints on the resulting dark-matter phase-space distribution. In
particular, this distribution need not be thermal -- it can even be
multi-modal, exhibiting a non-trivial pattern of peaks and troughs as a
function of momentum. We then proceed to show how these features can induce
modifications to the matter power spectrum. Finally, we assess the extent to
which one can approach the archaeological "inverse" problem of deciphering the
properties of an underlying dark sector from the matter power spectrum. Indeed,
one of the main results of this paper is a remarkably simple conjectured
analytic expression which permits the reconstruction of many of the important
features of the dark-matter phase-space distribution directly from the matter
power spectrum. Our results therefore provide an interesting toolbox of methods
for learning about, and potentially constraining, the features of non-minimal
dark sectors and their dynamics in the early universe.
