Local Axion Cosmic Strings from Superstrings

Axionic cosmic string solutions are investigated in a superstring motivated model with a pseudo-anomalous U(1) gauge symmetry. The inclusion of a gauge field and spatially varying dilaton allow local defect solutions with finite energy per unit length to be found. Fermion zero modes (whose presence is implied by supersymmetry) are also analysed. The corresponding fermion currents suggest strong cosmological bounds on the model. It is shown that the unusual form of the axion strings weakens these bounds. Other cosmological constraints on the underlying theory are also discussed.