Evolution of Generic Varying-Tension Cosmic Strings in Expanding Spacetimes

TL;DR

This paper investigates the dynamics of cosmic strings with time-dependent tensions in expanding universes, using numerical and machine learning methods to analyze non-circular loops near the Hubble scale, revealing their complex evolution.

Contribution

It extends previous analytic work by numerically studying non-circular string loops with varying tension, demonstrating their dynamics are equivalent to fixed-tension strings in a modified universe.

Findings

Non-circular loops can grow and percolate when tension decreases.

Dynamics are mathematically equivalent to fixed-tension strings in a modified scale factor.

Numerical and machine learning methods effectively explore complex string behaviors.

Abstract

It has recently been realised that strings with time-dependent tensions exhibit interesting dynamics; in particular, when the tension decreases loops of string can grow and possibly percolate. We extend previous analytic studies of strings with time-dependent tensions to numerical studies of non-circular loops. We show that the dynamics of a varying-tension string in expanding universe is mathematically equivalent to the evolution of a fixed-tension string in a universe with a modified scale factor. We use numerical solvers and machine learning techniques to explore the dynamics of non-circular string loops with radii close to the Hubble scale.