Lecture
This lecture covers the concept of instantons, focusing on non-perturbative effects in quantum field theory. The slides discuss examples of instantons, such as meta-stable states and the double well potential, highlighting the tunneling probability and exact eigenstates. The Euclidean propagator and semiclassical approximations for the path integral are explained, emphasizing the dominance of the lowest energy states. The presentation also delves into the classical solutions and stationary paths related to instantons, leading to considerations of multi-instanton solutions and dilute instantons in the gas approximation.