High speed collision and reconnection of Abelian Higgs strings in the
  deep type-II regime
  We study high speed collision and reconnection of cosmic strings in the
type-II regime (scalar-to-gauge mass ratios larger than one) of the Abelian
Higgs model. New phenomena such as multiple reconnections and clustering of
small scale structure have been observed 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 sufficiently large beta =
m_scalar^2/m_gauge^2. Here we give a more detailed account of our study,
involving 3D numerical simulations with beta in the range 1 to 64, the largest
value simulated to date, as well as 2D simulations of vortex-antivortex (v-av)
collisions to understand the possible relation to the new 3D phenomena. Our
simulations give further support to the idea that Abelian Higgs strings never
pass through each other, unless this is the result of a double reconnection;
and that the critical velocity (v_c) for double reconnection goes down with
increasing mass ratio, but energy conservation suggests a lower bound around
0.77c. 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 v-av
collisions in the form of radiating bound states. In the deep type-II regime
the angular dependence of v_c for double reconnection does not seem to conform
to semi-analytic predictions based on the Nambu-Goto approximation. We model
the high angle collisions reasonably well by incorporating the effect 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 effective collision angle is smaller because of the torque.
Our results suggest differences in network evolution and radiation output with
respect to the predictions based on Nambu-Goto or beta = 1 Abelian Higgs
dynamics.
