String Necklaces and Primordial Black Holes from Type IIB Strings
  We consider a model of static cosmic string loops in type IIB string theory,
where the strings wrap cycles within the internal space. The strings are not
topologically stabilised, however the presence of a lifting potential traps the
windings giving rise to kinky cycloops. We find that PBH formation occurs at
early times in a small window, whilst at late times we observe the formation of
dark matter relics in the scaling regime. This is in stark contrast to previous
predictions based on field theoretic models. We also consider the PBH
contribution to the mass density of the universe, and use the experimental data
to impose bounds on the string theory parameters.
