On thermal production of self-interacting dark matter
  We consider thermal production mechanisms of self-interacting dark matter in
models with gauged $Z_3$ symmetry. A complex scalar dark matter is stabilized
by the $Z_3$, that is the remnant of a local dark $U(1)_d$. Light dark matter
with large self-interaction can be produced from thermal freeze-out in the
presence of SM-annihilation, SIMP and/or forbidden channels. We show that dark
photon and/or dark Higgs should be relatively light for unitarity and then
assist the thermal freeze-out. We identify the constraints on the parameter
space of dark matter self-interaction and mass in cases that one or some of the
channels are important in determining the relic density.
