We report the first observation of multiple intercommutation ( more than two successive reconnections ) of cosmic strings at ultra-high collision speeds , and the formation of “ kink trains ” with up to four closely spaced left- or right-moving kinks .
We performed a flat space numerical study of abelian Higgs cosmic string intercommutation in the type-II regime \beta > 1 ( where \beta = m ^ { 2 } _ { scalar } / m ^ { 2 } _ { gauge } ) up to \beta = 64 , the highest value investigated to date .
Our results confirm earlier claims that the minimum critical speed for double reconnection goes down with increasing \beta , from \sim 0.98 c at \beta = 1 to \sim 0.86 c for \beta = 64 .
Furthermore , we observe a qualitative change in the process leading to the second intercommutation : if \beta \geq 16 it is mediated by a loop expanding from the collision point whereas if 1 < \beta \leq 8 the previously reported “ loop ” is just an expanding blob of radiation which has no topological features and is absorbed by the strings .
The multiple reconnections are observed in the loop-mediated , deep type-II regime \beta \geq 16 .
Triple reconnections appear to be quite generic for collision parameters on the boundary between single and double reconnection .
For \beta = 16 we observe quadruple events .
They result in clustering of small scale structure in the form of “ kink trains ” .
Our findings suggest that , due to the core interactions , the small scale structure and stochastic gravitational wave background of abelian Higgs strings in the strongly type-II regime may be quite different from what would be expected from studies of Nambu-Goto strings or of abelian Higgs strings in the \beta \approx 1 regime .