Extracting spinning two-body observables from S-matrix

by Prof. Canxin Shi (施灿欣) (ITP CAS)

Friday 7 Nov 2025, 23:00 → Saturday 8 Nov 2025, 01:00 Asia/Shanghai

1502 (四牌楼校区逸夫建筑馆丘成桐中心)

High-precision prediction of the two-body problem is at the center of gravitational waves physics. I will present a novel method for extracting observables for two-body scattering systems from a set of generating functions, with full spin dependence. The approach uses the classical limit of the logarithm of the quantum S-matrix as generating functions. The 4-point matrix element of Log(S) gives the radial action, corresponding to conservative effects, whereas the higher-point contributions encode radiative information. Different observables, such as momentum impulse, orbital angular momentum, and waveform, are uniformly obtained by from the generating functions. We demonstrate its power by calculating new high-precision results, including the impulse and spin kick for a probe in Kerr up to O(G^6 s^4), and the change in angular momentum for generic masses up to O(G^2 s^11). Via analytic continuation, we can also provide information about bound orbits, such as their fundamental frequencies.