Stretching and Kibble scaling regimes for Hubble-damped defect networks

TL;DR

This paper investigates how strong Hubble damping influences the evolution of topological defect networks, revealing new non-relativistic scaling regimes and validating these findings with high-resolution simulations.

Contribution

It introduces and characterizes new non-relativistic scaling regimes for defect networks under strong Hubble damping, supported by analytic modeling and high-resolution simulations.

Findings

Hubble damping can induce non-relativistic linear scaling regimes.

Identification of conformal stretching and Kibble regimes for defect networks.

High-resolution simulations confirm the analytic predictions.

Abstract

The cosmological evolution of topological defect networks can broadly be divided into two stages. At early times they are friction-dominated due to particle scattering and therefore non-relativistic, and may either be conformally stretched or evolve in the Kibble regime. At late times they are relativistic and evolve in the well known linear scaling regime. In this work we show that a sufficiently large Hubble damping (that is a sufficiently fast expansion rate) leads to a linear scaling regime where the network is non-relativistic. This is therefore another realization of a Kibble scaling regime, and also has a conformal stretching regime counterpart which we characterize for the first time. We describe these regimes using analytic arguments in the context of the velocity-dependent one-scale model, and we confirm them using high-resolution $4096^3$ field theory simulations of domain wall networks. We also use these simulations to improve the calibration of this analytic model for the case of domain walls.