Interaction of U(1) cosmic strings: Numerical intercommutation

The putative ability of cosmic strings to act as seeds for galaxies depends on the efficiency of a number of processes that produce an initial network of strings and then allow them to evolve to a population that can act as condensation centers. Here the classical field theory of the interaction of cosmic strings is studied. A limited survey of numerical evolutions has been carried out. Calculations have been carried out showing parallel string–string repulsion; string–antistring (i.e., antiparallel string) annihilation with initial velocity v=0 and v=0.75; string–string collision at right angles with v/c=0.1, 0.5, 0.75, 0.85, 0.9c, with v/c=0.75 at θ=π/4 and at θ=3π/4, and with v/c=0.9 at θ=7π/8; and string–string and string–antistring collisions with v/c=0.9 and v/c=0.95. Intercommutation occurs in all situations so far investigated except that string–antistring collision with v/c≳0.90 apparently leads to reemergence, i.e., no intercommutation. All simulations have a ‘‘sombrero’’ potential V (φ)=λ(‖φ‖²−σ²)² and a gauge field coupling e. (The numerical results are obtained with λ=0.01, e=0.2, giving the gauge field a slightly longer scale length than that of the scalar field.)