Infrared Finite Cross Sections and S-matrix elements

Abstract: Quantum field theory (QFT) works remarkably well for making theoretical predictionsin collider scattering experiments. One of the fundamental objects in thesecalculations, the scattering matrix (S-matrix), is inspired by a well definedoperator in non-relativistic quantum mechanics, but is plagued with bothultraviolet (UV) and infrared (IR) divergences in QFT. The UV divergences arenow understood through the program of renormalization, but IR divergencesremain an active area of research. We have explored three approaches toameliorate the problem of IR divergences, which will all be discussed in thistalk: i) The cross section method, ii) modification of the S-matrix, and iii)the coherent state formalism. The minimal set of processes required for afinite cross section as dictated by the KLN theorem will be elaborated on, alongwith examining a new approach based on factorization to define finite S-matrixelements in theories with massless particles and its connection to coherentstates.

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