Cosmic Strings and Cooper Pairs
  It is shown that it is possible for bound fermions on a cosmic string to form a superconducting state. Due to the attractive force between them, particles moving in opposite directions along the string form bound pairs. This involves a similar mechanism to superconductivity in metals at low temperatures. The method of Gorkov is used to analyse the system. In contrast to the situation in metals, the unusual properties of the string fermion spectrum allow a massless Abelian gauge field to provide the required attractive force. This results in far stronger superconductivity than usual. A massive gauge field can also be used, in which case the standard results apply. 
Stephen C. Davis