Investigating dark matter substructure with pulsar timing: II. Improved
  limits on small-scale cosmology
  Ultracompact Minihalos (UCMHs) have been proposed as a type of dark matter
sub-structure seeded by large-amplitude primordial perturbations and
topological defects. UCMHs are expected to survive to the present era, allowing
constraints to be placed on their cosmic abundance using observations within
our own Galaxy. Constraints on their number density can be linked to conditions
in the early universe that impact structure formation, such as increased
primordial power on small scales, generic weak non-Gaussianity, and the
presence of cosmic strings. We use new constraints on the abundance of UCMHs
from pulsar timing to place generalised limits on the parameters of each of
these cosmological scenarios. At some scales, the limits are the strongest to
date, exceeding those from dark matter annihilation. Our new limits have the
added advantage of being independent of the particle nature of dark matter, as
they are based only on gravitational effects.
