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Princeton Series in Physics Edited byPhilip W.Anderson, Arthur S. Wlghtman, and Sam B. Trelman Quantum Mechanics for Flamiltonians Defined as Quadratic Forms byBarry Simon Lectureson Current Algebra and Its Applications bySam B. Trelman. Roman Jackiw, and David). Gross PhysicalCosmology byPIE. Peebles TheMany-Worlds Interpretation of Quantum Mechanics editedby B. S. DeWitt and N. Graham HomogeneousRelativistic Cosmologies by MichaelP. Ryan. Jr. • and Lawrence C. Shepley TheP(4), Euclidean (Quantum) Field Theory byBarry Simon Studiesin Mathematical Physics: Essays in Honor of Valentine Bargmann editedby Elliott H. Lieb, B. Simon. and A. S. Wightman Convexityin the Theory of Lattice Oases byRobert B. Israel Workson the Foundations of Statistical Physics byN. S. Krylov Surprisesin Theoretical Physics byRudolf Peierls TheLarge-Scale Structure or the Universe byPiE. Peebles StatisticalPhysics and the Atomic Theory of Matter. From Boyle and Newton to Landau and Onsager byStephen G. Brush QuantumTheory and Measurement editedby John Archibald Wheeler and Wajcierh Hubert Zurek CurrentAlgebra and Anomalies bSam B. Treiman. Roman Jackiw. Bruno Zamino. and Edward Witten Quantumfluctuations byE. Nelson SpinOlasses and Other Frustrated Systems byDebashish Chowdhury (Spin Glasses and Other Frustrated Systems ispublished in co-operation with World Scientifte Publishing Co. Pte. Ltd., Singapore.) Large-Scale Motions in the Universe: A Vatican Study Week editedby Vera C. Rabin and George V. Coyne. S.). Instabilitiesand Fronts in Extended Systems byPierre Collet and Jean-Pierre Lckmann FromPerturbative to Constructive Renormalization byVincent Rtvasseau Maxwell'sDemon: Entropy. Information. Computing editedby haney S. Leff and Andrew F. Rex MoreSurprises in Theoretical Physics byRudolf PeierLs Supcrsymmetryand Supergravity. Second Edition. Revised and Expanded by Jul:u.sWess and Jonathan Bagger Introductionto Algebraic and Constructive Quantum Field Theory /n JohnC'.Rae:. Irving E. Segal. and ZhengJang Zhou Introduction to Algebraic and Constructive Quantum Field Theory JOHN C. BAEZ IRVING E. SEGAL ZHENGFANG ZHOU PRINCETON UNIVERSITY PRESS PRINCETON.NEW JERSEY Copyright © 1992 by Princeton University Press Publishedby PrincetonUniversity Press, 41 William Street, Princeton, New Jersey 08540 Inthe United Kingdom: Princeton University Press, Oxford All Rights Reserved Library of Congress Cataloging-in-Publication Data Baez,JohnC.,1961- Introductionto algebraic and constructive quantum field theory I byJohn C. Baez, irving E. Segal, Zhengfang Zhou. p. cm. —(Princetonseries in physics) Includes bibliographical references and index. ISBN 0-691-08546-3 I. Quantum field theory. 2. I. Segal, Irving Ezra. 11. Thou, Zhengfang, 1959- .ill.Title. IV. Series. QC174.45.B291991 530.1'43—dc2O 91-16504 C1P This book has been composed in Linotron Times Roman Princeton University Press books are printed on acid-free paper, and meet the guidelines for permanence and durability of the Committee on Production Guidelines for Book Longevity of the Council on Library Resources Printed in the United States of America by Princeton University Press, Princeton, New Jersey 10 9 8 7 6 5 4 3 2 1 Designedby Laury A. Egan Contents Preface ix Introduction xiii 1. The Free Boson Field 3 1.1.introduction 3 1.2.Weyl and Heisenberg systems 4 1.3.Functional integration 15 1.4.Quasi-invariant distributions 25 1.5. Absolute continuity 30 1.6.Irreducibility and ergodicity 37 1.7.The Fourier-Wiener transform 41 1.8.The structure of r and wave-particle duality 47 1.9.Implications of wave-particle duality 57 1.10. Characterization of the free boson field 62 1.11. The complex wave representation 64 1.12. Analytic features of the complex wave representation 70 2. The Free Fermion Field 75 2.1.Clifford systems 75 2.2.Existence of the free fermion field 80 2.3.The real wave representation 82 2.4.The complex wave representation 89 3. Properties of the Free Fields 96 3.1.Introduction 96 3.2.The exponential laws 97 3.3.Irreducibility 99 3.4.Representation of the orthogonal group by measure- preserving transformations 100 Contents 3.5. Bosonic quantization of symplectic dynamics 105 3.6. Fermionic quantization of orthogonal dynamics 113 4. AbsoluteContinuityand Unitary Implementabllity 118 4.1.Introduction 118 4.2.Equivalence of distributions 119 4.3.Quasi-invariant distributions and Weyl systems 121 4.4.Ergodicity and irreducibility of Weyl pairs 124 4.5.infinite products of Hubert spaces 125 4.6.Afflne transforms of the isonormal distribution 130 4.7.Implementability of orthogonal transformations on the fermion field 135 5. Quantizatlon 142 5.1.introduction 142 5.2.Weyl algebras over a linear sympleclic space 143 5.3.Regular states of the general boson field 147 5.4.The representation-independent Clifford algebra 149 5.5.Lexicon: The distribution of occupation numbers 150 6. Quantization of Linear Differential Equations 153 6.1.lntroduction 153 6.2.The Schrödingcrequation 154 6.3.Quantization of second-order equations 158 6.4.Finite propagation velocity 160 6.5.Quantization of the Dirac equation 162 6.6.Quantization of global spaces of wave functions 168 7. Renormalized Products of Quantum Fields 174 7.1.The algebra of additive renormalization 174 7.2.Renormalized products of' the free boson field 184 7.3.Regularity properties of boson field operators 190 7.4.Renormalized local products of field operators 200 Contents 8. ConstructIon of Nonlinear Quantized Fields 208 8.1. Introduction 208 8.2.The 210 8.3.Renormalized products at fixed time 214 8.4.Properties of fixed-time renormalization 223 8.5.The semigroup generated by the interaction Hamiltonian 227 8.6.The pseudo-interacting field 229 8.7.Dynamic causality 233 8.8.The local quantized equation of motion 237 Appendix A Principal Notations 251 Appendix B Universal Fields and the Quantization of Wave EquatIons 254 Glossary 258 Bibliography 281 Index 289 Preface This book is an amplified and updated version of a graduate course given by one of us (lEs)atvarious times during the past two decades. Ills intended as a rigorous treatment from first principles of the algebraic and analytic core of general quantum field theory. The first half of the book develops the alge- braictheorycentering around boson and fermion fields, their particle and wave representations, considerations of unitary implementability. and the represen- tation-independent formalism. This is tied in with the infinite- dimensional unitary, symplectic, and orthogonal groups, and their actions as canonical transformations on corresponding types of fields, in part, this rep- resents a natural extension of harmonic analysis and aspects of the theory of classical Lie groups from the finite to the infinite-dimensional case. But certain features that are crucial in the physical context—stability(positivityof the energy or of particle numbers) and causality (finiteness of propagation veloc- ity), both of which play essential roles in the quantization of wave equations— are also central in our treatment. These features are integrated with symmetry considerations in a coherent way that defines the essence of algebraic quantum field theory and subsumes the quantization of linear wave equations of a quite general type. But the key process that distinguishes quantum from classicalphysicsis that of particleproduction. Themathematical description of this phenomenon in accordance with the physical desiderata underlined above is, at the funda- mental level, by quantized nonlinearwaveequations. The algebraic theory developed in the first part of the book is used extensively in the second part in developing the mathematical interpretation, and solution in a prototypical Coil- text,of such equations. New analytic, rather than algebraic, issues of rcnor- malization and singular perturbation arise in this connection. In particular, nonlinear local functions of quantum fields—such as fields that are not neces- sarily free, or defined over arbitrary Riemannian manifolds—are treated in general contexts. These are in the direction of ultimate extension to physically more realistic cases than the model treated here. This consists of the formula- tion of the concept of solution of a quantized local nonlinear scalar wave equa- tion in a sense that is independent of the existence of an associated free held. and of the establishment of such solutions in two space-time dimensions (al- beit by a technique that starts from a free field). This book is intended as a self-contained introduction, and not as a treatise or compendium of results. A logically coherent and detailed treatment of a x Preface subject as indivisible and multifaceted as quantum field theory must be highly selective. We eschew both "practical" and the now classical "axiomatic" quantum field theory, on which there are excellent textbooks. Those in axio- matic theory include the authoritative texts by Bogolioubov, Logunov, and Todorov (1975); Jost (1965); and Streater and Wightman (1964). The pleni- tude of texts on practical theory includes the lucid treatments, in order of in- creasing scope, of Mandl (1959); Bjorken and Drell (1965); and Cheng and Li (1984). We also fail to do justice to the geometrical side of the theory, partly be- cause to do so would require another volume of the present size, but also because our approach is designed to apply in essence to virtually arbitrary geometries, the particularities of which need not be specified. Applications and illustrations are usually given in terms of Minkowski space, because this is