Decay of Cosmic Global String Loops

Abstract: We numerically study the decay of cosmic global string loops due to radiation of Goldstone bosons and massive scalar ($\chi$) particles. The length of loops we study range from 200-1000 times the width of the string core. We find that the lifetime of a loop is $\approx 1.4 L$. The energy spectrum of Goldstone boson radiation has a $k^{-1}$ fall off, where $k$ is the wavenumber, and a sharp peak at $k \approx m_\chi/2$, where $m_\chi$ is the mass of $\chi$. The latter is a new feature and implies a peak at high energies (MeV-GeV) in the cosmological distribution of QCD axions.

• The paper demonstrates that cosmic global string loops decay with a lifetime of about 1.4 times their length, based on detailed numerical simulations.
• It reveals that the energy spectrum of radiated Goldstone bosons follows a k⁻¹ fall-off and uncovers a sharp spectral peak at k ≈ mχ/2 for massive scalar emissions.
• These insights offer significant implications for axion cosmology, suggesting that decay-induced spectral features may critically influence dark matter models and observational strategies.

Decay of Cosmic Global String Loops

The paper "Decay of Cosmic Global String Loops" by Saurabh, Vachaspati, and Pogosian presents a comprehensive numerical investigation into the dynamic behavior and decay patterns of cosmic global string loops. The study explores the emission characteristics of both massless Goldstone bosons and massive scalar particles, denoted as $\chi$. The research aims to elucidate the complexities surrounding these string loops, vital for understanding certain cosmological phenomena, including axion production relevant to the strong CP problem.

Key Findings and Methodology

The authors utilized numerical simulations to explore loops ranging from 200 to 1000 times the width of the string core, allowing for the study of longer loops compared to previous studies. One of the definitive results from the study is the lifetime of the loops, found to be approximately $\tau \approx 1.4 L$, where $L$ denotes the loop size. This finding, determined through simulations considering loop sizes potentially relevant to cosmology, suggests efficiency in decay through radiative processes.

A significant aspect of the paper is the focus on the energy spectrum of radiated Goldstone bosons, which exhibits a $k^{-1}$ fall off. The study also uncovers a new spectral feature, a sharp peak at $k \approx m_\chi/2$, indicating enhanced energy levels corresponding to QCD axions, potentially impacting their cosmological distribution. This indicates that as loops decay, they emit massive $\chi$ particles that eventually decay further into Goldstone bosons, affecting the spectral characteristics.

Implications and Considerations

The findings have several implications for the understanding of cosmological models that incorporate axions. The inclusion of both massless and massive radiation offers a more holistic view of energy distribution contributing to dark matter density. The sharp spectral feature at high energies could also have profound implications for models dealing with axions as solutions to the strong CP problem, suggesting that future and current observational strategies should account for such features.

The study advances the understanding of cosmic strings by extending simulations to cases more representative of cosmological scenarios, providing insight into practical conditions that can produce various observable phenomena. The observed logarithmic divergence related to Goldstone radiation suggests that the size of the loop critically influences energy distribution, hence potentially affecting cosmological axion observations.

Prospects for Further Research

The results pave the way for further research into more diverse cosmic settings and longer timescales. Future studies might explore the backreaction of Goldstone boson radiation on string dynamics more thoroughly, and consider the integration of additional cosmological variables that were not included in the current study. The analytical techniques employed also have potential applications in addressing other unresolved issues in theoretical and observational cosmology, particularly in refining the models of dark matter constituents and factors affecting their detection.

In summation, the paper provides a robust analytical framework and set of results that significantly contribute to understanding the decay dynamics of cosmic global strings and their implications for modern cosmological models. The focus on both massless and massive emissions, along with the introduction of novel spectral features, marks a valuable step forward in cosmic string theory and its application to realistic cosmological scenarios.