Pinching instabilities in superconducting strings

TL;DR

This paper investigates the conditions under which superconducting cosmic strings develop pinching instabilities, introducing an improved analysis method that extends understanding beyond previous approximations and confirms stability of large vortons.

Contribution

The authors develop a refined analysis for pinching instabilities in superconducting strings, applicable to small wavelength perturbations, and validate it with simulations, expanding the known parameter space of instability.

Findings

Pinching instabilities occur over a larger parameter range than previously thought.

Electric strings can also exhibit pinching instabilities.

Large vortons are stable against all classical perturbations.

Abstract

Superconducting cosmic strings can exhibit longitudinal, pinching instabilities in some regions of the parameter space. We make predictions about the onset of this instability using the thin string approximation (TSA) and develop an improved analysis that remains applicable for small wavelength perturbations, where the TSA breaks down. We use simulations of perturbed strings to assess the accuracy of the TSA, test the predictions of our new analysis and demonstrate an improvement over previous methods in the literature. Notably, it appears that the instabilities are typically present for a larger range of magnetic strings than previously expected, and we show examples of pinching instabilities also occurring in electric strings. However, both our simulations and predictions agree that strings near the chiral limit are free from pinching instabilities and in particular our results support our previously published claim that vortons can be stable to all classical perturbations if they are sufficiently large.