In this seminar, I will begin with a brief review of high-energy scattering in QCD, covering the origin of the Balitsky–Fadin–Kuraev–Lipatov (BFKL) equation, the role of Pomeron exchange in cross sections, and the necessity of multi-Reggeon contributions. I will then turn to planar N=4 supersymmetric Yang–Mills theory, reviewing the structure of two-Reggeon exchange and its description in terms of a quantum system evolving in rapidity. Finally, I will present our recent progress on three-Reggeon exchange, including its emergence in specific kinematic regions and its impact on eight-point amplitudes. I will conclude by discussing new constraints arising from three-Reggeon exchange and outlining some open questions.

Inviter: Song He