Year: 2026
Type: preprint
Abstract: In this thesis we study the high-energy and collinear behaviour of gravitational scattering amplitudes and their relation to classical scattering and radiation observables. Multi-Regge kinematics, characterised by a strong rapidity ordering, provides the factorised building blocks governing the leading logarithmic structure. Relaxing this ordering to next-to-multi-Regge kinematics allows two neighbouring particles to have comparable rapidities and provides the real emission building blocks entering at next-to-leading logarithmic accuracy. We extract the next-to-multi-Regge impact factor from tree-level MHV amplitudes for pure gravitons and derive its gravitational splitting functions. We then use BCFW recursion relations to reconstruct the five-point tree amplitude for two massive scalars scattering with the emission of one graviton. Its high-energy limit yields the massive scalar--graviton impact factor and, through the KMOC formalism, a representation of the leading high-energy collinear waveform. Finally, by sewing the relevant vertices across unitarity cuts, we construct the elastic \(H\) kernel, its radiative extension and a classical next-to-multi-Regge kernel. The latter reproduces the standard \(H\) kernel in the multi-Regge limit and the universal Weinberg current in the soft limit.
Source: arXiv (Cornell University)
Author: Pietrini, Lorenzo
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funder: Sapienza Università di Roma
OpenAlex ID: W7220955134