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Abstract:
In quantum field theories, scattering amplitudes are calculated perturbatively by using the plane wave solustion of the equation of motion of participating particles and its Green's functions (propagators). In gauge theories, Green's functions for the gauge particles are found only after gauge fixing. The most popular method is covariant gauge fixing, including Feynman, Landau and R_\xi gauges. The common feature among all covariant gauges is to constrain the total derivative of gauge fields, \del_mu A(x)^\mu. Accordingly, all four helicity components of virtual gauge bosons are allowed to propagate (three in Landau gauge) in each Feynman diagram, leading to subtle cancellation among interfering diagrams to obtain physically observable scattering amplitudes.
In this seriese of four lectures, I will introudce the Feynman Diagram (FD) gauge, in which the scalar component of the helicity states of virtual gauge bosons are not allowed to propagate (in case of massless gauge bosons of QED and QCD), or replaced by the Goldstone boson (in case of massive weak bosons). We have modified the helicity amplitude calculation code (HELAS) inside MadGraph that allows us to obtain arbitrary tree-level scattering amplitudes in the FD gauge, for the SM and BSM models with SMEFT operators. No subtle cancellation among interfering amplitudes remain, and we can understand how individual diagrams interfer.
It is clear that the FD gauge allows us to obtain physical amplitudes for each individual Feynman diagram. We do not yet know why this is the case. I would like to explain my own thoughts on the problem, and how it can contribute to the radiative correction frameworks
of the SM, QCD and the EW theory.
Biography:
PhD: (Tokyo Metropolitan U, 1979)
Postdoc: (Univ. of Tokyo 1979-1981,
Univ. of Wisconsin-Madison 1981-1984,
DESY 1984-86, Durham 1989-1992)
Staff: (KEK 1986-2016) Retired: 2016
Alternative online link: https://meeting.tencent.com/dm/Df0Y6oLKIRm1
ID: 689553664