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 eciency of axionic dark matter abundance. The string network dynamics depend on the string intercommutation eciency (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 signicant role in their intercommutation dynamics. We also point out a subtlety in treating intercommutation of very nearly antiparallel strings numerically. We nd that the global strings of a O(2)- breaking scalar theory do intercommute for all physically relevant angles and velocities.