Residual Non-Abelian Dark Matter and Dark Radiation
  We propose a novel particle physics model in which vector dark matter (VDM)
and dark radiation (DR) originate from the same non-Abelian dark sector. We
show an illustrating example where dark $SU(3)$ is spontaneously broken into
$SU(2)$ subgroup by the nonzero vacuum expectation value of a complex scalar in
fundamental representation of $SU(3)$. The massless gauge bosons associated
with the residual unbroken $SU(2)$ constitute DR and help to relieve the
tension in Hubble constant measurements between $\textit{Planck}$ and Hubble
Space Telescope. In the meantime, massive dark gauge bosons associated with the
broken generators are VDM candidates. Intrinsically, this non-Abelian VDM can
interact with non-Abelian DR in the cosmic background, which results in a
suppressed matter power spectrum and leads to a smaller $\sigma_8$ for
structure formation.
