Beyond WIMPs: the Quark (Anti) Nugget Dark Matter
  We review a testable dark matter (DM) model outside of the standard WIMP
paradigm. The model is unique in a sense that the observed ratio $\Omega_{\rm
dark} \simeq \Omega_{\rm visible}$ for visible and dark matter densities finds
its natural explanation as a result of their common QCD origin when both types
of matter (DM and visible) are formed during the QCD transition and both are
proportional to single dimensional parameter of the system, $\Lambda_{\rm
QCD}$. We argue that the charge separation effect also inevitably occurs during
the same QCD transition in the presence of the $\cal{CP}$ odd axion field
$a(x)$. It leads to preferential formation of one species of nuggets on the
scales of the visible Universe where the axion field $a(x)$ is coherent. A
natural outcome of this preferential evolution is that only one type of the
visible baryons (not anti- baryons) remain in the system after the nuggets
complete their formation. Unlike conventional WIMP dark matter candidates, the
nuggets and anti-nuggets are strongly interacting but macroscopically large
objects. The rare events of annihilation of the anti-nuggets with visible
matter lead to a number of observable effects. We argue that the relative
intensities for a number of measured excesses of emission from the centre of
galaxy (covering more than 11 orders of magnitude) are determined by standard
and well established physics. At the same time the absolute intensity of
emission is determined by a single new fundamental parameter of the theory, the
axion mass, $10^{-6} {\rm eV} \lesssim m_a \lesssim 10^{-3}{\rm eV}$. Finally,
we comment on implications of these studies for the axion search experiments,
including microwave cavity and the Orpheus experiments.
