The Physics of Soft Particles

Henriette Elvang, Associate Professor of Physics, University of Michigan

The scattering cross-section is the key observable in particle physics experiments, such as the Large Hadron Collider at CERN. In quantum field theory, the cross-section is expressed in terms of the scattering amplitude, which traditionally is calculated as a sum of Feynman diagrams. When many particles are involved in a process – as for example in multi-gluon scattering -- the Feynman diagram approach becomes very difficult, even at leading order (tree-level). In recent years, it has been realized that amplitudes possess a very interesting mathematical structure that can be exploited to find more efficient calculational methods. Not assuming prior knowledge of quantum field theory or Feynman rules, I will review the background and recent progress in this exciting field of research.