The S-matrix is a fundamental object in quantum field theory, relating theoretical predictions to data from collider experiments. However, in theories with massless particles when interactions between single-particle states prevail at asymptotic times, the S-matrix is infrared (IR) divergent in perturbation theory. In this talk, we explore three solutions to the IR divergence problem: i) summing over initial and final states to obtain a finite cross section, ii) modifying the S-operator, and iii) using coherent states as scattering states. In particular, we exploit the universality of asymptotic evolution to define a modified S-operator in theories with massless particles. The resulting S-matrix can be interpreted as Wilson coefficients in Soft-collinear effective theory, as remainder functions in N=4 super Yang-Mills theory, or as coherent states. Examining its analytic structure thus provides a new probe of familiar objects from scattering calculations..

Per partecipare su Zoom, collegarsi al meeting
Topic: Theory and Pheno seminars
https://infn-it.zoom.us/j/8573185271
Meeting ID: 857 318 5271