Intercommutation of U(1) global cosmic strings
  Global strings (those which couple to Goldstone modes) may play a role in
cosmology. In particular, if the QCD axion exists, axionic strings may control
the efficiency of axionic dark matter abundance. The string network dynamics
depend on the string intercommutation efficiency (whether strings re-connect
when they cross). We point out that the velocity and angle in a collision
between global strings "renormalize" between the network scale and the
microscopic scale, and that this plays a significant role in their
intercommutation dynamics. We also point out a subtlety in treating
intercommutation of very nearly antiparallel strings numerically. We find that
the global strings of a O(2)-breaking scalar theory do intercommute for all
physically relevant angles and velocities.
