In theories with cosmic strings, a small fraction of string loops may collapse to form black holes. In this paper, various constraints on such models involving black holes are considered. Hawking radiation from black holes, gamma and cosmic ray flux limits and constraints from the possible formation of stable black hole remnants are reanalyzed. The constraints which emerge from these considerations are remarkably close to those derived from the normalization of the cosmic string model to the cosmic microwave background anisotropies.

• Received 14 July 1997

DOI:https://doi.org/10.1103/PhysRevD.57.2158