发表机构
International Centre for Theoretical Physics Asia-Pacific (ICTP-AP); University of Chinese Academy of Sciences (UCAS); Taiji Laboratory for Gravitational Wave Universe; King’s College London, University of London; University of Florida; University of Notre Dame; Johannes Gutenberg-Universität Mainz; The Hong Kong University of Science and Technology（亚太理论物理中心; 中国科学院大学; 太极引力波宇宙实验室; 伦敦大学国王学院; 佛罗里达大学; 圣母大学; 美因茨约翰内斯古腾堡大学; 香港科技大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究统一了宇宙弦引力波背景的谐波与爆发谱形式体系，实现多频带联合贝叶斯推断，并用NANOGrav、EPTA和LVK数据约束四个环分布模型，增强LVK界限并改进弦张力限制。
AI 中文摘要
宇宙弦环产生宽带引力波背景（GWB），通常通过两种不同的形式体系进行建模：离散谐波展开（常用于脉冲星计时阵列（PTA）研究）和连续爆发叠加（用于地面GWB搜索）。在本工作中，我们正式统一了这两种形式体系，表明它们提供了同一潜在辐射过程的离散和连续表示，并在尺度不变的谱平台上收敛。在上升的低频分支上，前几个谐波占主导，离散性质变得重要，导致两种形式体系出现分歧。在这一统一框架内，谱计算在频带间更加一致，从而能够进行多频带推断。利用这一物理见解，我们使用NANOGrav、EPTA和LIGO–Virgo–KAGRA（LVK）数据集，对四个代表性的环分布模型进行联合贝叶斯推断。通过联合采样弦张力$G\mu$以及平均尖点和扭结数$\{N_c, N_k\}$，考虑了环辐射的不确定性。我们发现，对于其中三个模型，采用谐波展开将LVK约束增强了$21\\%-31\\%$。此外，严格的LVK约束排除了其中三个模型解释观测到的PTA共同信号的可能性。对于唯一幸存的模型，我们的多频带分析改进了对$G\mu$的推断限制。
英文摘要
Cosmic-string loops generate a broadband gravitational-wave background (GWB) that is typically modeled via two distinct formalisms: a discrete harmonic expansion, commonly used in pulsar-timing-array (PTA) studies, and a continuous burst superposition, employed in ground-based GWB searches. In this work, we formally unify the two formalisms, showing that they provide discrete and continuous representations of the same underlying radiation process and converge on the scale-invariant spectrum plateau. On the rising low-frequency branch, where the first few harmonics dominate, the discrete nature becomes important, causing the two formalisms to diverge. Within this unified framework, the spectral calculation is more consistent across frequency bands, enabling multi-band inference. Leveraging this physical insight, we perform joint Bayesian inference across four representative loop-distribution models using the NANOGrav, EPTA, and LIGO--Virgo--KAGRA (LVK) datasets. By jointly sampling the string tension $Gμ$ alongside the average cusp and kink numbers $\{N_c, N_k\}$, the loop-radiation uncertainties are accounted for. We find that employing the harmonic expansion strengthens the LVK bounds by $21\%-31\%$ for three of these models. Additionally, the stringent LVK bounds preclude three of these models from explaining the observed PTA common signal. For the sole surviving model, our multi-band analysis improves the inferred limit on $Gμ$.
Comments6 pages, 2 figures, plus Supplemental Material (14 pages, 5 figures)
