Speaker: Neil Christensen
Title: Challenges with Internal Photons in Constructive QED
Room: 3024
Zoom: https://zoom.us/j/186024391
Host: Da Liu
Abstract:
A new approach to calculating scattering amplitudes constructively with spinors and recursive formula that bypass field theory and Feynman diagrams and are trivially gauge invariant has been emerging over recent decades. Most of the early work in this area focused on purely massless theories, but recently it was shown how to naturally extend this constructive formalism to massive theories by generalizing the helicity spinors to spin spinors, objects that transform under a direct product of the Lorentz group and the spin group. With this progress, we have been building spinor amplitudes for the Standard Model and comparing the results with Feynman diagrams at all energies, with the hope that they might improve the efficiency of matrix-element generators in the future. Although we have had success for multiple processes, we have run into trouble with diagrams with internal photons (and external massive lines). In this talk, we focus on the process e,ebar->mu,mubar in QED, a very simple process with only one diagram. We discuss the result coming from the current constructive approach and note that it does not agree with Feynman diagrams. We then find the correct result and discuss why the current constructive method might not work for this particular case. It is our hope that this will encourage the community to overcome this challenge so that the potential of constructive amplitudes can be fully realized.
