Classical Observables from Feynman Amplitudes

Abstract

We study KMOC formalism developed to calculate classical observables from amplitudes in Quantum Field Theory. Amplitudes and S-matrix carry the information of interaction of any scattering process and thus the classically observed quantities should be attainable from them .We try to show some new calculations regarding the angular momentum impulses via this formalism which led to some interesting results. We studied the non-conservation of angular momentum classically and understand the phenomenon.We studied Faddev Kulish states that account for long range interactions of states and try to apply them to KMOC formalism.We then studied the seminal papers by Weinberg on soft photons and gravitons and look at the idea of these states arising from soft photons.Some results regarding the validity of classical soft photon was also reviwed in context of angular momentum radiated during collision.We then also study the S-matrix and its infrared divergence problem . We saw how the dressings of Faddev Kulish states cancel these divergences in the S-Matrix. The dressings are known to be coherent states of photons and the equivalence between S-matrix and these states has been explored.