Primordial black holes as biased tracers
  Primordial black holes (PBHs) are theoretical black holes which may be formed
during the radiation dominant era and, basically, caused by the gravitational
collapse of radiational overdensities. It has been well known that in the
context of the structure formation in our Universe such collapsed objects,
e.g., halos/galaxies, could be considered as bias tracers of underlying matter
fluctuations and the halo/galaxy bias has been studied well. Employing a
peak-background split picture which is known to be a useful tool to discuss the
halo bias, we consider the large scale clustering behavior of the PBH and
propose an almost mass-independent constraint to the scenario that dark matters
(DMs) consist of PBHs. We consider the case where the statistics of the
primordial curvature perturbations is almost Gaussian, but with small
local-type non-Gaussianity. If PBHs account for the DM abundance, such a large
scale clustering of PBHs behaves as nothing but the matter isocurvature
perturbation and constrained strictly by the observations of cosmic microwave
backgrounds (CMB). From this constraint, we show that, in the case a certain
single field causes both CMB temperature perturbations and PBH formations, the
PBH-DM scenario is excluded even with quite small local-type non-Gaussianity,
$|f_\mathrm{NL}|\sim\mathcal{O}(0.01)$, while we give the constraints to
parameters in the case where the source field of PBHs is different from CMB
perturbations.
