Introduction to Many-Body Theory: From Action Principles to Path Integrals and Functional Methods (UNITEXT for Physics)

This textbook provides a self-contained introduction to many-body theory that bridges the gap between the standard graduate curriculum and more research-oriented courses in many-body theory.The author systematically constructs the basic formalism of many-body theory, starting from Newton's second law, and subsequently develops action principles and symmetry-based techniques.Upon switching to quantum theory, second quantization and the Feynman path integral are introduced.After a treatment of statistical mechanics from an information-entropy perspective, which allows for a simple understanding of temperature dependent variational principles, the book switches to a coherent state path-integral formulation.This approach makes diagrammatic perturbation theory, linear response techniques, and renormalization group methods, which are treated in later parts of the book, accessible to a broad audience. The content of the book is based on a set of lectures on the Quantum Theory of Solids that t