Higher order intercommutations in Cosmic String Collisions

Abstract

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 $\beta =m_{scalar}^2/m_{gauge}^2$) 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 $\sim 0.98c$ at $\beta =1$ to $\sim 0.86c$ for $\beta =64$. Furthermore, we observe a qualitative change in the process leading to the second intercommutation: if $\beta \ge 16$ it is mediated by a loop expanding from the collision point whereas if $1<\beta \le 8$ 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 $\beta \ge 16$. 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.

5 pages, 4 figures, Accepted for publication by PRL

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• Weak lensing of CMB by cosmic (super-)strings
• Ultra-relativistic oscillon collisions
• Intercommutation of U(1) global cosmic strings
• Topological invariants for superconducting cosmic strings
• Dynamical simulations of colliding superconducting strings
• Tackling tangledness of cosmic strings by knot polynomial topological invariants