Global cosmic strings are generically predicted in particle physics beyond the Standard Model, e.g., a post-inflationary global $U\left(1\right)$ symmetry breaking which may associate with axion-like dark matter. We demonstrate that although subdominant to Goldstone emission, gravitational waves (GWs) radiated from global strings can be observable with current/future GW detectors. The frequency spectrum of such GWs is also shown to be a powerful tool to probe the Hubble expansion rate of the Universe at times prior to the Big Bang nucleosynthesis where the standard cosmology has yet to be tested.

中文翻译：

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全球宇宙弦的随机引力波背景

全局宇宙弦通常在标准模型之外的粒子物理学中进行预测，例如，通货膨胀后的全局 $ü（\mathrm{1个}）$对称性破坏，可能与类似轴突的暗物质有关。我们证明，尽管主要是Goldstone辐射，但可以使用当前/将来的GW探测器观察到从整体弦辐射的重力波（GWs）。此类GW的频谱也被证明是在尚未进行标准宇宙学测试的大爆炸核合成之前的某个时间探测宇宙哈勃扩展速率的强大工具。