Cosmic string loop shapes

TL;DR

This paper studies the shapes of cosmic string loops from simulations, modeling gravitational back reaction through smoothing, and finds that loops are mainly straight segments with kinks, rarely cusps, and smoothing often introduces cusps without fragmenting loops.

Contribution

It provides a detailed analysis of cosmic string loop shapes from simulations and models gravitational back reaction effects through smoothing, revealing the typical structure and cusp formation.

Findings

Loops are mainly straight segments separated by kinks.

Smoothing often introduces cusps on loops.

Loops generally do not fragment after smoothing.

Abstract

We analyze the shapes of cosmic string loops found in large-scale simulations of an expanding-universe string network. The simulation does not include gravitational back reaction, but we model that process by smoothing the loop using Lorentzian convolution. We find that loops at formation consist of generally straight segments separated by kinks. We do not see cusps or any cusp-like structure at the scale of the entire loop, although we do see very small regions of string that move with large Lorentz boosts. However, smoothing of the string almost always introduces two cusps on each loop. The smoothing process does not lead to any significant fragmentation of loops that were in non-self-intersecting trajectories before smoothing.