Proliferation of sharp kinks on cosmic (super-)string loops with junctions

TL;DR

This paper investigates how kinks on cosmic super-string loops with junctions proliferate, leading to an exponential increase in sharp kinks, which impacts gravitational wave signals, with numerical simulations supporting the findings.

Contribution

It demonstrates the exponential growth of sharp kinks on cosmic string loops with junctions and analyzes their evolution through numerical simulations.

Findings

Sharp kink proliferation can lead to exponential growth in kink sharpness.

Loops develop several orders of magnitude of sharp kinks before junction collision.

Proliferation may be halted by junction collision or gravitational backreaction.

Abstract

Motivated by their effect on the gravitational wave signal emitted by cosmic strings, we study the dynamics of kinks on strings of different tensions meeting at junctions. The propagation of a kink through a Y-junction leads to the formation of three `daughter' kinks. Assuming a uniform distribution of the incoming wave vectors at the junction, we find there is a significant region of configuration space in which the sharpness of at least one of the daughter kinks is enhanced relative to the sharpness of the initial kink. For closed loops with junctions we show this leads to an exponential growth in time of very sharp kinks. Using numerical simulations of realistic, evolving cosmic string loops with junctions to calculate the distribution of kink amplitudes as a function of time, we show that loops of this kind typically develop several orders of magnitude of very sharp kinks before the two junctions collide. This collision, or other effects such as gravitational backreaction, may end the proliferation.