New CMB constraints for Abelian Higgs cosmic strings

TL;DR

This paper uses advanced numerical simulations of Abelian Higgs cosmic strings to refine constraints on their tension from CMB data, demonstrating improved modeling techniques and confirming the robustness of previous results.

Contribution

It introduces enhanced simulation methods for cosmic strings, leading to more accurate CMB power spectra and tighter constraints on string tension compared to earlier studies.

Findings

Revised upper limit on string tension: Gμ < 2.0×10⁻⁷ at 95% confidence

Improved simulation volume reduces uncertainties in power spectrum amplitude

Field theory simulations now sufficiently accurate for CMB calculations

Abstract

We present cosmic microwave background (CMB) power spectra from recent numerical simulations of cosmic strings in the Abelian Higgs model and compare them to CMB power spectra measured by Planck. We obtain revised constraints on the cosmic string tension parameter $G\mu$. For example, in the $\Lambda$CDM model with the addition of strings and no primordial tensor perturbations, we find $G\mu < 2.0 \times 10^{-7}$ at 95% confidence, about 20% lower than the value obtained from previous simulations, which had 1/64 of the spatial volume. We investigate the source of the difference, showing that the main cause is an improved treatment of the string evolution across the radiation-matter transition. The increased computational volume also makes possible to simulate fully the physical equations of motion, in which the string cores shrink in comoving coordinates. This, and the larger dynamic range, changes the amplitude of the power spectra by only about 10%, demonstrating that field theory simulations of cosmic strings have now reached the required dynamic range for CMB calculations.