Fixed Energy Propagator: Analytic Structure

This lecture covers the concept of the fixed energy propagator as a Green function, focusing on its analytic structure and application in the context of a free theory. The instructor explains the key properties and calculations involved in determining the fixed energy propagator, including the retarded propagator and its relation to eigenvalues and eigenfunctions. Various methods for computing the propagator are discussed, emphasizing the importance of continuous spectrum considerations. The lecture also delves into integrated density of states and the computation of the propagator for different scenarios.