Echoes of Global Cosmic Strings

TL;DR

This paper investigates the cosmological signatures of global cosmic strings, focusing on their decay into Nambu-Goldstone bosons and the resulting observable effects on the universe's structure and background radiation.

Contribution

It provides a comprehensive analysis of the detectability of Nambu-Goldstone bosons from global cosmic strings using current and future cosmological observations.

Findings

Constraints on Nambu-Goldstone boson mass and symmetry-breaking scale derived from cosmological data.

Predictions for the sensitivity of upcoming CMB missions to these particles.

Assessment of the impact of global cosmic strings on matter power spectrum and dark radiation.

Abstract

If the Universe underwent a cosmic phase transition, it may have left behind a network of cosmic strings. When these strings arise from the breaking of a gauge symmetry, their decay produces a significant stochastic background of gravitational waves. In contrast, if they originate from the breaking of a global symmetry, their decay predominantly yields Nambu-Goldstone bosons, which can persist as dark matter or dark radiation. In this work, we assess the detectability of this particle spectrum using a range of cosmological probes. We employ semi-numerical methods to estimate the resulting energy density and compute the associated matter power spectrum. We then compare these predictions with observations of the cosmic microwave background, Lyman-$\alpha$ forest, large-scale structure surveys, and the UV luminosity function, thereby deriving constraints on the Nambu-Goldstone boson mass and the symmetry-breaking scale. Finally, we present projections for the sensitivity of upcoming cosmic microwave background missions.