Exploring the Universe with Dark Light Scalars
  We study the cosmology of the dark sector consisting of (ultra) light
scalars. Since the scalar mass is radiatively unstable, a special explanation
is required to make the mass much smaller than the UV scale. There are two
well-known mechanisms for the origin of scalar mass. The scalar can be
identified as a pseudo-Goldstone boson, whose shift symmetry is explicitly
broken by non-perturbative corrections, like the axion. Alternatively, it can
be identified as a composite particle like the glueball, whose mass is limited
by the confinement scale of the theory. In both cases, the scalar can be
naturally light, but interaction behavior is quite different. The lighter the
axion (glueball), the weaker (stronger) it interacts. We consider the dark
axion whose shift symmetry is anomalously broken by the hidden non-abelian
gauge symmetry. After the confinement of the gauge group, the dark axion and
the dark glueball get masses and both form multicomponent dark matter. We
carefully consider the effects of energy flow from the dark gluons to the dark
axions and derive the full equations of motion for the background and the
perturbed variables. The effect of the dark axion-dark gluon coupling on the
evolution of the entropy and the isocurvature perturbations is also clarified.
Finally, we discuss the gravo-thermal collapse of the glueball subcomponent
dark matter after the halos form, in order to explore the potential to
contribute to the formation of seeds for the supermassive black holes observed
at high redshifts. With the simplified assumptions, the glueball subcomponent
dark matter with the mass of $0.01-0.1 {\rm MeV}$, and the axion main dark
matter component with the decay constant $f_a={\cal O}(10^{15}-10^{16}){\rm
GeV}$, the mass of ${\cal O}(10^{-14}-10^{-18})\,{\rm eV}$, can provide the
hint on the origin of the supermassive black holes at high redshifts.
