探索LISA与ET协同作用下的宇宙引力波背景
Exploring cosmological gravitational wave backgrounds through the synergy of LISA and ET
AI总结：
本文研究LISA和ET引力波探测器协同观测，提出综合灵敏度与新型信噪比，以多频段探测宇宙引力波背景，揭示早期宇宙膨胀及高阶关联函数特征。
摘要：
引力波干涉仪LISA和ET预计将在未来十年内投入运行，可能大致同时进行。它们将在不同的频率范围内运行，对随机引力波背景（SGWB）振幅具有相似的综合灵敏度。我们研究了这两个探测器之间的协同作用，涉及对具有大振幅和宽频率谱的宇宙学SGWB的多频段探测。我们发展了综合灵敏度的概念，并提出了一种新的信噪比（SNR），该信噪比最适合于表征同时运行的LISA和ET干涉仪系统的几何特性。通过研究各种SGWB示例，如宇宙学相变、宇宙弦、原始暴胀产生的SGWB，我们表明LISA和ET同时运行将有机会更有效地评估同一宇宙学源产生的引力波谱特征，但在不同的频率尺度上。此外，这两个实验串联运行可以对大爆炸核合成（BBN）之前的早期宇宙膨胀特征敏感，这些特征影响SGWB频率分布，而否则无法探测到，因为两个不同的频率范围对应于两个不同的BBN前（或暴胀后）时期。除了考虑引力波谱外，我们还对LISA和ET对高阶张量关联函数软极限的灵敏度进行了初步研究。鉴于这些实验在不同的频段运行，它们的协同作用构成了对高阶引力波关联函数压缩极限的理想直接探针，而仅使用单一仪器无法测量这些极限。
英文摘要：
The gravitational wave (GW) interferometers LISA and ET are expected to be functional in the next decade(s), possibly around the same time. They will operate over different frequency ranges, with similar integrated sensitivities to the amplitude of a stochastic GW background (SGWB). We investigate the synergies between these two detectors, in terms of a multi-band detection of a cosmological SGWB characterised by a large amplitude, and a broad frequency spectrum. We develop the notion of integrated sensitivity and propose a novel signal-to-noise (SNR) optimal for characterization of the geometrical properties of the interferometer systems of LISA and ET operating simultaneously. By investigating various examples of SGWBs, such as those arising from cosmological phase transition, cosmic string, primordial inflation, we show that LISA and ET operating together will have the opportunity to assess more effectively the characteristics of the GW spectrum produced by the same cosmological source, but at separate frequency scales. Moreover, the two experiments in tandem can be sensitive to features of early universe cosmic expansion before big-bang nucleosynthesis (BBN), which affects the SGWB frequency profile, and which would not be possible to detect otherwise, since two different frequency ranges correspond to two different pre-BBN (or post-inflationary) epochs. Besides considering the GW spectrum, we additionally undertake a preliminary study of the sensitivity of LISA and ET to soft limits of higher order tensor correlation functions. Given that these experiments operate at different frequency bands, their synergy constitutes an ideal direct probe of squeezed limits of higher order GW correlators, which can not be measured operating with a single instrument only.
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