High speed collision and reconnection of Abelian Higgs strings in the deep type-II regime

We study the high speed collision and reconnection of Abrikosov{Nielsen{Olesen cosmic strings in the type-II regime of the Abelian Higgs model, that is, scalar-to-gauge mass ratios larger than one. Qualitatively new phenomena such as multiple reconnections and clustering of small scale structure have been observed in the deep type-II regime and reported in a previous paper, as well as the fact that the previously observed \loop" that mediates the second intercommutation is only a loop for suciently large mass ratios. Here we give a more detailed account of our study, which involves 3D numerical simulations with the parameter = m 2=m 2 in the range 1 64, the largest value simulated to date, as well as 2D simulations of vortex-antivortex head-on collisions to understand their possible relation to the new 3D phenomena. Our simulations give further support to the idea that Abelian Higgs strings never pass through each other, even at ultrarelativistic speeds, unless this is the result of a double reconnection; and that the critical velocity for double reconnection goes down with increasing mass ratio, but energy conservation suggests a lower bound around 0.77 c. We discuss the qualitative change in the intermediate state observed for large mass ratios. We relate it to a similar change in the outcome of 2D vortex{antivortex collisions in the form of radiating bound states, whereas we nd no evidence of the back-to-back reemergence reported in previous studies. In the deep type-II regime the angular dependence of the critical speed for double reconnection does not seem to conform to the semi-analytic predictions based on the Nambu-Goto approximation. We can model the high angle collisions reasonably well by incorporating the eect of core interactions, and the torque they produce on the approaching strings, into the Nambu{Goto description of the collision. An interesting, counterintuitive aspect is that the eective collision angle is smaller (not larger) as a result of the torque. Our results suggest dierences in network evolution and radiation output with respect to the predictions based on Nambu{Goto or = 1 Abelian Higgs dynamics.