Quantum Effective Action

This lecture introduces the concept of the quantum effective action, explaining how it is related to the correlators in momentum space and how it can be used to organize perturbation theory calculations. The instructor covers the derivation of the effective action from the classical action, the role of connected correlators, and the significance of exact vertices and propagators in the quantum action. The lecture also delves into the properties of the effective action under derivatives, the connection to the Lippmann-Schwinger equation, and the importance of momentum space in understanding the structure of correlators. Additionally, the instructor discusses the calculation of correlators in Euclidean and Minkowski space, highlighting the importance of counter terms in renormalizing the theory.