BBN constraints on MeV-scale dark sectors. Part I. Sterile decays
  We study constraints from Big Bang Nucleosynthesis on inert particles in a
dark sector which contribute to the Hubble rate and therefore change the
predictions of the primordial nuclear abundances. We pay special attention to
the case of MeV-scale particles decaying into dark radiation, which are neither
fully relativistic nor non-relativistic during all temperatures relevant to Big
Bang Nucleosynthesis. As an application we discuss the implications of our
general results for models of self-interacting dark matter with light
mediators.
