Constraining the early universe with primordial black holes
  In this thesis, the effect of non-Gaussianity upon the abundance of
primordial black holes (PBHs), and the implications of such an effect are
considered. It is shown that even small non-Gaussianity parameters can have a
large effect on the constraints that can be placed on the primordial curvature
perturbation power spectrum - which can become stronger or weaker by an order
of magnitude. The effects of super-horizon curvature perturbation modes at the
time of PBH formation are considered, and it is shown that these have little
effect on the formation of a PBH, but can have an indirect effect on the
abundance of PBHs due to modal coupling to horizon-scale modes in the presence
of non-Gaussianity. By taking into account the effect of modal coupling to
CMB-scale modes, many models can be ruled out as a mechanism to produce enough
PBHs to constitute dark matter.
