Effective non-intercommutation of local cosmic strings at high collision speeds

TL;DR

This paper investigates the high-speed collision behavior of cosmic strings, demonstrating that they can pass through each other via double intercommutation, with thresholds depending on string type and collision angle.

Contribution

The study provides numerical evidence and a simple model explaining double intercommutation in cosmic strings at ultra-high speeds, including new insights into threshold velocities and effects of string type.

Findings

Strings pass through each other at high speeds due to double intercommutation.

Threshold speeds are approximately 0.97c for type I and 0.90c for deep type II strings.

A second effect involving loop formation can lower the critical velocity for double intercommutation.

Abstract

We present evidence that Abrikosov-Nielsen-Olesen (ANO) strings pass through each other for very high speeds of approach due to a double intercommutation. In near-perpendicular collisions numerical simulations give threshold speeds bounded above by $\sim 0.97 c$ for type I, and by $\sim 0.90 c$ for deep type II strings. The second intercommutation occurs because at ultra high collision speeds, the connecting segments formed by the first intercommutation are nearly static and almost antiparallel, which gives them time to interact and annihilate. A simple model explains the rough features of the threshold velocity dependence with the incidence angle. For deep type II strings and large incidence angles a second effect becomes dominant, the formation of a loop that catches up with the interpolating segments. The loop is related to the observed vortex - antivortex reemergence in two-dimensions. In this case the critical value for double intercommutation can become much lower.