Applications of On-shell Techniques to The Standard Model and Beyond

Abstract

Lagrangians, fields and Feynman diagrams are losing their monopoly on particle physics. A recent alternative, collectively referred to as `on-shell techniques', has proven itself as not only a method to compute scattering amplitudes more efficiently, but also as a tool to unlock underlying structures of quantum theories previously obscured by traditional approaches. The Standard Model (SM) of particle physics, the best particle description of our world today, is a quantum field theory (QFT) based model. With on-shell methods on the rise, as well the recent ability to deal with massive particles, the time has come to see these techniques make contact with the SM. In this thesis, we use on-shell techniques to construct, describe, and push amplitudes across different scales, a journey which leads us to discover various on-shell analogs of QFT and string results. In particular, we explain the Higgs mechanism and spontaneous symmetry breaking, and derive all the relevant physics in generic theories as well as in the SM. In addition, we examine a class of string-inspired UV completions of the SM and place constraints on them. These results make no reference to Lagrangians or quantum fields, and so, present a new avenue to probe the SM and beyond.