Collisions of strings with Y junctions

Abstract

We study the dynamics of Nambu--Goto strings with junctions at which three strings meet. In particular, we exhibit one simple exact solution and examine the process of intercommuting of two straight strings, in which they exchange partners but become joined by a third string. We show that there are important kinematical constraints on this process. The exchange cannot occur if the strings meet with very large relative velocity. This may have important implications for the evolution of cosmic superstring networks and non-abelian string networks.Comment: 4 pages, 1 figure, uses revtex 4. Clarifying comments added to correct a conceptual error, reference updated. Version accepted by Phys Rev Letters, with additional references and minor change