Praise for the first edition “Quantum field theory is an extraordinarily beautiful subject, but it can be an intimidating one. The profound and deeply physical concepts it embodies can get lost, to the beginner, amidst its technicalities. In this book, Zee imparts the wisdom of an experienced and remarkably creative practitioner in a user-friendly style. I wish something like it had been available when I was a student.” —Frank Wilczek, Massachusetts Institute of Technology “Finally! Zee has written a ground-breaking quantum field theory text based on the course I made him teach when I chaired the Princeton physics department. With utmost clarity he gives the eager student a light-hearted and easy-going introduction to the multifaceted wonders of quantum field theory. I wish I had this book when I taught the subject.” —Marvin L. Goldberger, President, Emeritus, California Institute of Technology “This book is filled with charming explanations that students will find beneficial.” —Ed Witten, Institute for Advanced Study “This book is perhaps themost user-friendly introductory text to the essentials of quantum field theory and its many modern applications. With his physically intuitive approach, ProfessorZeemakes a serious topicmore reachable for beginners, reducing the conceptual barrier while preserving enough mathematical details necessary for a firm grasp of the subject.” —Bei Lok Hu, University of Maryland “Like the famous Feynman Lectures on Physics, this book has the flavor of a good blackboard lecture. Zee presents technical details, but only insofar as they serve the larger purpose of giving insight into quantum field theory and bringing out its beauty.” —Stephen M. Barr, University of Delaware “This is a fantastic book—exciting, amusing, unique, and very valuable.” —Clifford V. Johnson, University of Durham “Tony Zee explains quantum field theory with a clear and engaging style. For budding or seasoned condensed matter physicists alike, he shows us that field theory is a nourishing nut to be cracked and savored.” —Matthew P. A. Fisher, Kavli Institute for Theoretical Physics “I was so engrossed that I spent all of Saturday and Sunday one weekend absorbing half the book, to my wife’s dismay. Zee has a talent for explaining the most abstruse and arcane concepts in an elegant way, using the minimum number of equations (the jokes and anecdotes help). . . . I wish this were available when I was a graduate student. Buy the book, keep it by your bed, and relish the insights delivered with such flair and grace.” —N. P. Ong, Princeton University What readers are saying “Funny, chatty, physical: QFT education transformed!! This text stands apart from others in so many ways that it’s difficult to list them all. . . . The exposition is breezy and chatty. The text is never boring to read, and is at times very, very funny. Puns and jokes abound, as do anecdotes. . . . A book which is much easier, and more fun, to read than any of the others. Zee’s skills as a popular physics writer have been used to excellent effect in writing this textbook. . . . Wholeheartedly recommended.” —M. Haque “A readable, and rereadable instant classic on QFT. . . . At an introductory level, this type of book—with its pedagogical (and often very funny) narrative—is priceless. [It] is full of fantastic insights akin to reading the Feynman lectures. I have since used QFT in a Nutshell as a review for [my] year-long course covering all of Peskin and Schroder, and have been pleasantly surprised at how Zee is able to preemptively answer many of the open questions that eluded me during my course. . . . I value QFT in a Nutshell the same way I do the Feynman lectures. . . . It’s a text to teach an understanding of physics.” —Flip Tanedo “One of those books a person interested in theoretical physics simply must own! A real scientific masterpiece. I bought it at the time I was a physics sophomore and that was the best choice I could have made. It was this book that triggeredmy interest in quantum field theory and crystallized my dreams of becoming a theoretical physicist. . . . The main goal of the book is tomake the reader gain real intuition in the field. Amazing . . . amusing . . . real fun. What also distinguishes this book from others dealing with a similar subject is that it is written like a tale. . . . I feel enormously fortunate to have come across this book at the beginning of my adventure with theoretical physics. . . . Definitely the best quantum field theory book I have ever read.” —Anonymous “I have used Quantum Field Theory in a Nutshell as the primary text. . . . I am immensely pleased with the book, and recommend it highly. . . . Don’t let the ‘damn the torpedoes, full steam ahead’ approach scare you off. Once you get used to seeing the physics quickly, I think you will find the experience very satisfying intellectually.” —Jim Napolitano “This is undoubtedly the best book I have ever read about the subject. Zee does a fantastic job of explaining quantum field theory, in a way I have never seen before, and I have read most of the other books on this topic. If you are looking for quantum field theory explanations that are clear, precise, concise, intuitive, and fun to read—this is the book for you.” —Anonymous “One of the most artistic and deepest books ever written on quantum field theory. Amazing . . . extremely pleasant . . . a lot of very deep and illuminating remarks. . . . I recommend the book by Zee to everybody who wants to get a clear idea what good physics is about.” —Slava Mukhanov “Perfect for learning field theory on your own—by far the clearest and easiest to follow book I’ve found on the subject.” —Ian Z. Lovejoy “A beautifully written introduction to the modern view of fields . . . breezy and enchanting, leading to exceptional clarity without sacrificing depth, breadth, or rigor of content. . . . [It] passes my test of true greatness: I wish it had been the first book on this topic that I had found.” —Jeffrey D. Scargle “A breeze of fresh air . . . a real literary gem which will be useful for students who make their first steps in this difficult subject and an enjoyable treat for experts, who will find new and deep insights. Indeed, the Nutshell is like a bright light source shining among tall and heavy trees—the many more formal books that exist—and helps seeing the forest as a whole! . . . I have been practicing QFT during the past two decades and with all my experience I was thrilled with enjoyment when I read some of the sections.” —Joshua Feinberg “This text not only teaches up-to-date quantum field theory, but also tells readers how research is actually done and shows them how to think about physics. [It teaches things that] people usually say ‘cannot be learned from books.’ [It is] in the same style as Fearful Symmetry and Einstein’s Universe. All three books . . . are classics.” —Yu Shi “I belong to the [group of ] enthusiastic laymen having enough curiosity and insistence . . . but lacking themastery of advancedmath and physics. . . . I really could not see the forest for the trees. But at long last I got this book!” —Makay Attila “More fun than any other QFT book I have read. The comparisons to Feynman’s writings made by several of the reviewers seem quite apt. . . . His enthusiasm is quite infectious. . . . I doubt that any other book will spark your interest like this one does.” —Stephen Wandzura “I’m having a blast reading this book. It’s both deep and entertaining; this is a rare breed, indeed. I usually prefer the more formal style (big Landau fan), but I have to say that when Zee has the talent to present things his way, it’s a definite plus.” —Pierre Jouvelot “Required reading for QFT: [it] heralds the introduction of a book on quantum field theory that you can sit down and read. My professor’s lectures made much more sense as I followed along in this book, because concepts were actually EXPLAINED, not just worked out.” —Alexander Scott “Not your father’s quantum field theory text: I particularly appreciate that things are motivated physically before their mathematical articulation. . . . Most especially though, the author’s ‘heuristic’ descriptions are the best I have read anywhere. From them alone the essential ideas become crystal clear.” —Dan Dill Q uantum Field Theory in a Nutshell This page intentionally left blank Q uantum Field Theory in a Nutshell SECOND EDITION A. Zee P R I N C E T O N U N I V E R S I T Y P R E S S . P R I N C E T O N A N D O X F O R D Copyright © 2010 by Princeton University Press Published by Princeton University Press, 41 William Street, Princeton, New Jersey 08540 In the United Kingdom: Princeton University Press, 6 Oxford Street, Woodstock, Oxfordshire OX20 1TW All Rights Reserved Library of Congress Cataloging-in-Publication Data Zee, A. Quantum field theory in a nutshell / A. Zee.—2nd ed. p. cm. Includes bibliographical references and index. ISBN 978-0-691-14034-6 (hardcover : alk. paper) 1. Quantum field theory. I. Title. QC174.45.Z44 2010 ′ 530.14 3—dc22 2009015469 British Library Cataloging-in-Publication Data is available This book has been composed in Scala LF with ZzT X E by Princeton Editorial Associates, Inc., Scottsdale, Arizona Printed on acid-free paper. press.princeton.edu Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 To my parents, who valued education above all else