Slightly Ultra-violet Freeze-in a Hidden Gluonic Sector
  The dark glueball (DGB) from a hidden Yang-Mills sector is a simple non-WIMP
dark matter candidate characterized by very few parameters. However, it suffers
the over dense issue. To overcome it, in general the dark sector is required to
be hierarchically cooler than the visible sector. To naturally generate the
desired hierarchy, in this paper we introduce higher dimensional operators
coupling the dark gauge field strength tensor to the standard model (SM) Higgs
doublets or gauge field strength tensors. By tracking the different phases of
the universe from the end of inflation, prethermalization, reheating to the
radiation dominance era, we show that these operators can make the DGB be a
viable dark matter candidate over a wide mass region, from the sub-GeV to
multi-PeV or even beyond. At the same time, these operators open decay channels
of DGB to the SM species, and partial of the parameter space could leave hints
in the cosmic ray.
