Title: Unitarity and the On-Shell Action of Worldline Quantum Field Theory Show Chinese title

Title: 单位性和世界线量子场论的在壳作用

Abstract: We develop the on-shell action formalism within Worldline Quantum Field Theory (WQFT) to describe scattering of spinning compact bodies in General Relativity in the post-Minkowskian (PM) expansion. The real on-shell action is constructed from vacuum diagrams with causal (retarded) propagators from which scattering observables such as momentum impulse and spin kick follow via Poisson brackets of the initial scattering data. Furthermore, we explore the implications of unitarity at the level of the worldline and show how generalised unitarity techniques can be adapted to WQFT to efficiently compute multi-loop contributions. Our work establishes a concrete link between WQFT and amplitude-based methods, elucidating how unitarity cuts ensure equivalence between the on-shell action derived from either approach. Extending the state-of-the-art, we complete the full on-shell action -- including dissipative terms -- at (formal) 3PM order and up to quartic spin interactions on both massive bodies. Show Chinese abstract

Abstract: 我们在世界线量子场论（WQFT）中发展了在壳作用量形式主义，以在后闵可夫斯基（PM）展开中描述广义相对论中自旋致密物体的散射。实数在壳作用量是从带有因果（迟滞）传播子的真空图构造的，通过初始散射数据的泊松括号得出如动量冲量和自旋冲击等散射可观测量。此外，我们探讨了世界线层面的幺正性含义，并展示了如何将广义幺正性技术适应于WQFT，以高效计算多环贡献。我们的工作建立了WQFT与基于幅度的方法之间的具体联系，阐明了幺正性切割如何确保从任一方法导出的在壳作用量之间的等价性。在现有技术的基础上，我们完成了完整的在壳作用量——包括耗散项——在（形式）3PM阶次以及在两个质量体上的四次自旋相互作用。