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Description
Quantum field theory (QFT) works remarkably well for making theoretical predictions in collider scattering experiments. One of the fundamental objects in these calculations, the scattering matrix (S-matrix), is inspired by a well defined operator in non-relativistic quantum mechanics, but is plagued with both ultraviolet (UV) and infrared (IR) divergences in QFT. The UV divergences are now understood through the program of renormalization, but IR divergences remain an active area of research. Three approaches can ameliorate the IR divergences, which will all be discussed in this talk: i) The cross section method, ii) the modification-of-S method, and iii) the coherent state formalism. We show how to exploit factorization properties to define a gauge invariant and infrared finite “hard” S-matrix, and explore its analytic properties. In particular, we discuss new relations between sequential discontinuities of amplitudes and multiple cuts through the corresponding Feynman diagrams, which imply the Steinmann relations when all external particles are massive.
Organised by
Cora Dvorkin
