Scattering-amplitude methods are revolutionizing our understanding of black-hole dynamics. To date, however, this program has focused primarily on black-hole scattering, while the merger regime has largely been regarded as beyond its reach. In this talk, I will present a framework aimed at extending the amplitude approach to this regime. I will first review how scattering waveforms are extracted from on-shell amplitudes and then introduce a new framework for merger radiation, in which a black-hole merger is formulated as an inclusive on-shell transition from two incoming black holes to a remnant accompanied by radiation. Following the logic of effective field theory, the construction separates the soft radiative sector from the unresolved hard dynamics of the merger, whose effects are encoded in effective on-shell transition data. No direct use is made of Einstein’s equations or geodesic equations. Instead, generalized unitarity, BCFW recursion, and soft theorems provide the central tools, yielding an effective S-matrix description of black-hole mergers grounded in modern particle-physics methods. As applications of this framework, I will show how it recovers key features of merger dynamics and radiation—including linear memory and the formation of the remnant angular momentum—while systematically accounting for recoil, nonlinear memory, and tail effects.
Brief biography:
Andrea Cristofoli is a theoretical physicist working at the intersection of scattering amplitudes, black-hole dynamics, and gravitational-wave physics. He completed his PhD at the Niels Bohr Institute in Copenhagen as a Marie Curie Fellow. He then joined the University of Edinburgh as a Research Associate before moving to the Yukawa Institute for Theoretical Physics at Kyoto University after being awarded a JSPS Fellowship. His research aims to reformulate classical gravity in the language of modern quantum field theory, deriving black-hole dynamics and gravitational radiation directly from scattering amplitudes.
Prof. Huaxing Zhu