High resolution calibration of the cosmic strings velocity dependent one-scale model

TL;DR

This paper provides a high-resolution calibration of the velocity-dependent one-scale (VOS) model for cosmic string evolution using advanced GPU simulations, analyzing the impact of numerical parameters and improving model reliability for different cosmological scenarios.

Contribution

It offers the most comprehensive calibration of the VOS model to date, exploring numerical sensitivities and identifying more reliable velocity estimators for cosmic string networks.

Findings

The conjugate momentum estimator is more reliable at high expansion rates.

Numerical parameters significantly influence VOS model calibration.

Results impact observational constraints on cosmic strings.

Abstract

The canonical velocity-dependent one-scale (VOS) model for cosmic string evolution must be calibrated using high resolution numerical simulations, We exploit our state of the art graphics processing unit accelerated implementation of the evolution of local Abelian-Higgs string networks to provide a detailed and statistically robust calibration of the VOS model. We rely on the largest set of high resolution simulations carried out to date, with a wide range of cosmological expansion rates, and explore the impact of key numerical parameters, including the dynamic range (comparing box sizes from $1024^3$ to $4096^3$), the lattice spacing, and the choice of numerical estimators for the string velocity. We explore the sensitivity of the VOS model parameters to these numerical parameters, with a particular emphasis on the observationally crucial loop chopping efficiency, and also identify key differences between the equation of state and conjugate momentum estimators for the string velocities, showing that the latter one is more reliable for fast expansion rates (while in Minkowski space the opposite has been previously shown). Finally, we briefly illustrate how our results impact observational constraints on cosmic strings.