The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band, with a particular focus on Ultra High-Frequency Gravitational Waves (UHF-GWs), covering the MHz to GHz range. The absence of known astrophysical sources in this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising gravitational sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of the workshop “Challenges and opportunities of high-frequency gravitational wave detection” held at ICTP Trieste, Italy in October 2019, that set up the stage for the recently launched Ultra-High-Frequency Gravitational Wave (UHF-GW) initiative.

LIGO 和 Virgo 合作首次直接测量引力波，为探索我们的宇宙开辟了新途径。本白皮书概述了在 LIGO/Virgo 频段以上频率的引力波搜索中预期的挑战和收益，特别关注覆盖 MHz 至 GHz 范围的超高频引力波 (UHF-GW)。在这个频率范围内没有已知的天体物理源为发现在早期和晚期宇宙中运行的标准模型之外的物理提供了一个独特的机会，我们重点介绍了一些最有希望的引力源。我们回顾了为应对这一挑战而提出的几个检测器概念，并将它们的预期灵敏度与各种模型中预测的信号强度进行比较。