Constraints on cosmic strings due to black holes formed from collapsed cosmic string loops

The cosmological features of primordial black holes formed from collapsed cosmic string loops are studied. Observational restrictions on a population of primordial black holes are used to restrict f, the fraction of cosmic string loops which collapse to form black holes, and μ, the cosmic string mass per unit length. Using a realistic model of cosmic strings, we find that the energy density in 100 MeV photons radiated by the black holes serves as the strongest restriction on the parameters, such that f≤10^-17 for Gμ=10^-6. We also find that inert black hole remnants left by black holes formed from collapsed cosmic string loops cannot serve as the dark matter. If earlier, crude estimates that f∼10^-12 are reliable, our results severely restrict μ, and therefore limit the viability of the cosmic string large-scale structure scenario.