Dark Radiation Alleviates Problems with Dark Matter Halos
  We show that a scalar and a fermion charged under a global U(1) symmetry can
not only explain the existence and abundance of dark matter (DM) and dark
radiation (DR), but also imbue DM with improved scattering properties at
galactic scales, while remaining consistent with all other observations.
Delayed DM-DR kinetic decoupling eases the missing satellites problem, while DR
mediated self-interactions of DM ease the cusp vs. core and too big to fail
problems. In this scenario, DM is expected to be pseudo-Dirac and have a mass
between 100 keV and 10 GeV. The predicted DR may be measurable using the
primordial elemental abundances from big bang nucleosynthesis (BBN), and using
the cosmic microwave background (CMB).
