Quantum tunneling of superconducting string currents
  We investigate the decay of current on a superconducting cosmic string through quantum tunneling. We construct the instanton describing tunneling in a simple bosonic string model, and estimate the decay rate. The tunneling rate vanishes in the limit of a chiral current. This conclusion, which is supported by a symmetry argument, is expected to apply in general. It has important implications for the stability of chiral vortons. 
Jose J. Blanco-Pillado, Ken D. Olum and Alexander Vilenkin