Energy-momentum correlations for Abelian Higgs cosmic strings

TL;DR

This paper presents advanced numerical simulations of Abelian Higgs cosmic strings, providing improved energy-momentum correlators crucial for understanding their impact on cosmic microwave background and matter perturbations.

Contribution

The study introduces four-fold increased simulation range, simulates strings with constant physical width across eras, and proposes a new, more accurate method for constructing source functions for cosmological models.

Findings

Correlators measured at horizon scale are more accurate.

Correlation functions evolve adiabatically across cosmological transitions.

New source function construction method improves accuracy and implementation.

Abstract

We report on the energy-momentum correlators obtained with recent numerical simulations of the Abelian Higgs model, essential for the computation of cosmic microwave background and matter perturbations of cosmic strings. Due to significant improvements both in raw computing power and in our parallel simulation framework, the dynamical range of the simulations has increased four-fold both in space and time, and for the first time we are able to simulate strings with a constant physical width in both the radiation and matter eras. The new simulations improve the accuracy of the measurements of the correlation functions at the horizon scale and confirm the shape around the peak. The normalization is slightly higher in the high wave-number tails, due to a small increase in the string density. We study for the first time the behaviour of the correlators across cosmological transitions, and discover that the correlation functions evolve adiabatically, ie the network adapts quickly to changes in the expansion rate. We propose a new method for constructing source functions for Einstein-Boltzmann integrators, comparing it with two other methods previously used. The new method is more consistent, easier to implement, and significantly more accurate.