| Abstract: | In recent years, our understanding of perturbative scattering amplitudes has advanced considerably, thanks to new "on-shell" methods. These methods can be much more efficient than Feynman diagrams because they exploit the underlying simplicity of scattering amplitudes, and recycle lower-loop information via the old principles of unitarity and factorization. They have shed new light on three areas: one-loop amplitudes with many external particles in quantum chromodynamics, for application to the physics of the Large Hadron Collider; multi-loop amplitudes in N=4 super-Yang-Mills theory (a cousin of QCD), where they unveiled a rich structure suggesting that the theory is solvable; and N=8 supergravity, where ultraviolet cancellations point to the possibility of a perturbatively finite theory of quantum gravity. Professor Dixon was one of the "fathers" of orbifold string compactifications, and played a key role in the effort to obtain standard-model like theories from String Theory. He then turned to the calculation of scattering amplitudes using, originally, string techniques, and later, general properties of the S-matrix. He has led the development of this field for a number of years now, with important results ranging from the calculation of QCD scattering at the LHC--a crucial ingredient for discovering new physics, to the finiteness of supersymmetric gravity theories--a subject of great controversy for 30 years. |
