Primordial black holes from cosmic necklaces

Cosmic necklaces are hybrid topological defects consisting of monopoles and strings. We argue that primordial black holes(PBH) may have formed from loops of the necklaces, if there exist stable winding states, such as coils and cycloops. Unlike the standard scenario of PBH formation from string loops, in which it has been suggested that the production ratio f becomes a tiny fraction f ∼ 10−20, the production ratio in our model is f ∼ 1. Although the result obtained in this paper depends on the evolution of the dimensionless parameter r, the existence of the winding state could be excluded in some cases. Since the existence of the winding state is due to the existence of a non-tivial circle in the compactified space, the PBH formation can be used to probe the structure of the compactified space of brane models. Black holes produced by this mechanism are interesting because they have peculiar properties.