Quantum Field Theory II: Cross Section & Lifetime

This lecture covers topics such as cross section, lifetime, quantum fluid, asymptotic states, discrete symmetries, normal ordering, and perturbation theory. It delves into the intricacies of quantum field theory, focusing on the proper split between different states and the challenges of perturbation theory beyond leading order. The instructor discusses the identification of split between different states, the LS procedure, and the delicate matter of defining proper splits. The lecture also touches upon the time-dependent perturbation theory and the importance of normal ordering in quantum field theory.