内容简介
The last few decades have seen major advances in the physics of elementary particles. New generations of particle accelerators and detectors have come into operation, and have successfully contributed to improving the quantity and quality of data on diverse interaction processes and to the discoveries of whole new families of particles. At the same time, important new ideas have emerged in quantum field theory, culminating in the developments of theories for the weak and strong interactions to complement quantum electrodynam-ics, the theory of the electromagnetic force. The simplest of the new theories that are at the same time mathematically consistent and physically successful constitute what is known as the standard model of the fundamental interac-tions. This book is an attempt to present these remarkable advances at an elementary level, making them accessible to students familiar with quantum mechanics, special relativity, and classical electrodynamics.
内页插图
目录
1 Particles and Interactions:An Overview
1.1 A Preview
1.2 Particles
1.2.1 Leptons
1.2.2 Quarks
1.2.3 Hadrons
1.3 Interactions
1.4 Symmetries
1.5 Physical Units
Problems
Suggestions for Further Reading
2 B080n Fields
2.1 Lorentz Symmetry
2.1.1 Lorentz TraIlsformations
2.1.2 Tensor Algebra
2.1.3 llensor Fields
2.2 Scalar Fields
2.2.1 Space-Time Translation of a Scalar Field
2.2.2 Lorentz Transformation of a Scalar Field
2.3 Vector Fields
2.4 The Klein-Gordon Equation
2.4.1 Free-Patticle Solutions
2.4.2 Particle Probability
2.4.3 Second Quantization
2.4.4 Operator Algebra
2.4.5 Physical Significance of the Fock Operators
2.5 Quantized Vector Fields
2.5.1 Maesive Vector Fields
2.5.2 The Maxwell Equations
2.5.3 Quantization of the Electromagnetic Field
2.5.4 Field Energy and Momentum
2.6 The Action
2.6.1 The Euler-Lagrange Equation
2.6.2 Conserved Current
Problems
Suggestions for Further Reading
3 Fermion Fields
3.1 The Dirac Equation
3.2 Lorentz Symmetry
3.2.1 Covariance of the Dirac Equation
3.2.2 Spin of the Dirac Field
3.2.3 Bilinear Covariants
3.3 Free.Particle Solutions
3.3.1 Normalized Spinors
3.3.2 Completeness Relations
3.3.3 Helicities
3.4 The Lagrangian for a Free Dirac Particle
3.5 Quantization of the Dirac Field
3.5.1 Spins and Statistics
3.5.2 Dirac Field Observables
3.5.3 F0ck Space
3.6 Zero-Mass Fermions
Problems
Suggestions for Further Reading
4 Collisions and Decays
4.1 Interaction Representation
4.1.1 The Three Pictures
4.1.2 Time E:volution in the Interaction Picture
4.1.3 The S.matrix
4.2 Cross.Sections and Decay Rares
4.2.1 General Formulas
4.2.2 Two-Body Reaction to Two-Body Final States
4.2.3 Decay Rates
4.3 Interaction Models
4.4 Decay Modes of Scalar Particles
4.4.1 Neutral Decay Mode
4.4.2 Charged Decay Mode
4.5 Pion Scattering
4.5.1 The Scalar Boson Propagator
4.5.2 Scattering Processes
4.5.3 Summary and Generalization
4.6 Electron-Proton Scattering
4.6.1 The Electromagnetic Interaction
4.6.2 Electron-Proton Scattering Cross-Section
4.7 Electron-Positron Annihilation
4.8 Compton Scattering
Problems
Suggestions for Further Reading
5 Discrete Symmetries
5.1 Parity
5.1.1 Parity in Quantum Mechanics
5.1.2 Parity in Field Theories
5.1.3 Parity and Interactions
5.2 Time Inversion
5.2.1 Time Inversion in Quantum Mechanics
5.2.2 Time Inversion in Field Theories
5.2.3丁and Interactions
5.3 Charge Conjugation
5.3.1 Additive Quantum Numbers
5.3.2 Charge Conjugation in Field Theories
5.3.3 Interactions
5.4 The CPT Theorem
5.4.1 Implications of CPT Invariance
5.4.2 C.P,T.and CPT
Problems
Suggestions for Further Reading
6 Hadtons and Isospln
6.1 Charge Symmetry and Charge Independence
6.2 Nucleon Field in Isospin Space
6.3 Pion Field in Isospin Space
6.4 G.Parity
6.4.1 Nucleon and Pion Fields
6.4.2 Other Unflavored Hadrons
6.5 Isospin of Strange Particles
6.6 Isospin Violations
6.6.1 Electromagnetic Interactions
6.6.2 Wlealc Interactions
Problems
Suggestions for Further Reading
7 Quarks and SU(3)Symmetry
7.1 Isospin:SU(2) Symmetry
7.2 Hypercharge:SU(31 Symmetry
7.2.1 The Fundamental Representation
7.2.2 Higher.Dimensional Representations
7.2.3 Physical Significance of F3 and F3
7.2.4 3×3*Equal Mesons
7.2.5 3×3×3 Equal Baryons
7.3 Mass Splitting of the Hadron Multiplets
7.3.1 Baryons
7.3.2 Mesons
7.4 Including Spin:SU(6)
7.4.1 Mesons
7.4.2 Baryons
7.4.3 Application:Magnetic Moments of Hadrons
7.5 The Color of Quarks
7.6 The New Particles
7.6.1 J/tf,and Charm
7.6.2 The TaU Lepton
7.6.3 From Bottom to ToP
Problems
Suggestions for Further Reading
8 Gauge Field Theories
8.1 Symmetries and Interactions
8.2 Abelian Gauge Invariance
8.3 Non.Abelian Gauge Invariance
8.4 Quantum Chromodynamics
8.5 Spontaneous Breaking of Global Symmetries
8.5.1 The Basic Idea
8.5.2 Breakdown ofDiscrete Symmetry
8.5.3 Breakdown of Abelian Symmetry
8.5.4 Breakdown of Non-Abelian Symmetry
8.6 Spontaneous Breaking ofLocal Symmetries
8.6.1 Abelian Symmetry
8.6.2 Non.Abelian Symmetry
Problems
Suggestions for Further Reading
9 The Standard Model of the Electroweak Interaction
9.1 The Wleak Interaction Before the Gauge Theories
9.2 Gauge.Invariant Model of One.Lepton Family
9.2.1 Global Symmetry
9.2.2 Gauge Invariance
……
精彩书摘
1.4 SymmetriesThe recent history of physics gives us several examples that illustrate theimportance of the symmetry considerations in explaining empirical observa.tions or in developing new ideas .Thus,the intriguing regularities found in the atomic periodic table can be naturally explained as resulting from the rotational symmetry that characterizes atoms in their ground states;similarly,the relativity theory owes the clarity and the elegance of its fornmlation toits guiding principle,Lorentz in variance .However,more than any other field,particle physics,perhaps because of the very nature of the subject or becauseof the absence of relevant macroscopic analogies or useful classical correspon.dences,has by necessity conferred upon the symmetry concept a key role that has become essential in fornmlating new theories.The existence of the Q-particle and the reality of quarks are two outstanding demonstrations of thepower of this line of reasoning.but no less impressive is the prediction of theexistence of the electronic neutrino by Wolfgang Pauli back in 1 930 solely onthe basis of the conservation of energy, momentum,and angular nlomentum,the validity of which was still in doubt at the time.Pauli took a road less traveled by and opened up a whole new world. The prominent place taken by the symmetry considerations throughout this book only reflects their importance in particle physics.In this section .we will sketch a general picture of the idea. and briefly define various symmetry operations. As we have seen above .every particle js identified by a set of quantumnumbers.These numbers summarize the intrinsic properties of the particleand,for this reason,are called the internal quantum numbers,meaning thatthey have nothing to do with the kinetic state of the particle.which is de.scribed by other conserved quantities that depend on the state the particleis in,such as the energy,momentum,or angular momentum. The existence of a quantum number in a system always arises from theinvariance of the system under a qlobal geometrical transformation.that is。one that does not depend on the coordinates of the space.time point whereit is applied.A simple example suffices to illustrate the general situation.Consider two particles in a refefence frame iu which their interaction energydepends only on the relative distance of the particles.It follows then,first,that a displacement of the origin of the coordinates by an arbitrary distanceproduces no measurable physical effects on the system,and second,that thetotal momentum of the system remains constant in time because its rate ofchange,given by the total gradient of the interaction energy,is strictly zero.So,generally.if we have a physicaI system in which the absolute positions arenot observable fits energy depending off the relative distance rather than in.dividual particle positionsl and if we apply on it a geometrical transformation(spatial translation),then we obtain as direct consequences the invariance ofthe systern to the applied transformation(translational invariance)and theexistence of a conservation rule fmomentum conservation).These are,inshort,the interdepelldent aspects found in every symmetry principle.
前言/序言
The last few decades have seen major advances in the physics of elementary particles. New generations of particle accelerators and detectors have come into operation, and have successfully contributed to improving the quantity and quality of data on diverse interaction processes and to the discoveries of whole new families of particles. At the same time, important new ideas have emerged in quantum field theory, culminating in the developments of theories for the weak and strong interactions to complement quantum electrodynam-ics, the theory of the electromagnetic force. The simplest of the new theories that are at the same time mathematically consistent and physically successful constitute what is known as the standard model of the fundamental interac-tions. This book is an attempt to present these remarkable advances at an elementary level, making them accessible to students familiar with quantum mechanics, special relativity, and classical electrodynamics.
The main content of the book is roughly divided into two parts; one on theories to lay the foundation and the other on further developments of concepts and descriptions of phenomena to prepare the student for more advanced work. After a brief overview of the subject and a presentation of some basic ideas, two chapters which deal mostly with relativistic one-body wave equations, quantization of fields, and Lorentz invariance follow. In the spirit of the practical approach taken in this book, a heuristic derivation of the Feynman rules is given in the fourth chapter, where the student is shown how to calculate cross-sections and decay rates at the lowest order.The following chapter contains a discussion on discrete symmetries and the concept of symmetry breaking. Isospin is introduced next as the simplest example of internal symmetries in order to ease the reader into the notion of unitary groups in general and of SU(3) in particular, which is discussed next together with the recent discoveries of new particles. The next two chapters present the standard model of the fundamental interactions. We make contact with experiments in subsequent chapters with detailed studies of some fundamental electroweak processes, such as the deep inelastic lepton-nucleon scattering, the CP violation in the neutral K mesons, the neutrino oscillations and the related problem of the solar neutrino deficit, and finally,the r lepton decay, which touch upon many aspects of weak interactions. The very high precision of the data that is now attained in some of these processes requires a careful examination of higher-order effects. This leads to a detailed study of one-loop QCD corrections to weak interactions. The next chapter demonstrates the remarkable property of asymptotic freedom of quantum chromodynamics and introduces the powerful concept of the renormalization group which plays a central role in many phenomena. The heavy flavors of quarks, which pose new questions on several aspects of interactions and could open windows on the new physics, form the subject of a separate chapter.We close with a review of the present status of the standard model and,briefly, of its extensions. Selected solutions to problems are given. Finally,important formulas are collected in an Appendix for convenient reference.
物理学的边界:探索宇宙的深层结构 本书将引导读者进入一个微观世界的奇妙领域,一个由看不见的、基本构成单元和它们之间复杂交织的作用力所主宰的领域。这不是对任何特定教材的重复,而是对粒子物理学这一迷人学科核心概念、实验发现和理论框架的深度剖析,重点在于构建对现代物理学图景的整体理解,而非对某一特定教科书内容的复述。 我们将从对“基本”的哲学和实验定义开始。什么是基本粒子?它们是构成物质的最小单元吗?我们如何通过实验手段,在宏观世界中探测到这些微小到令人难以想象的实体?本书不会拘泥于列举标准模型的粒子列表,而是深入探讨发现这些粒子的历史背景、实验技术的演进,以及每一次重大发现(如电子、质子、中子、中微子以及后来的夸克和希格斯玻色子)如何重塑了我们对物质本质的认知。 第一部分:物质的基石——粒子分类与对称性原理 本书首先构建一个理解粒子世界的框架,即粒子分类的系统性。我们不会仅仅停留在费米子和玻色子(物质粒子与媒介粒子)的简单二分法上。更关键的是,我们将探讨朗道-杨-米尔斯(Landau-Yang-Mills)理论背景下的内在对称性原理如何在粒子物理学中扮演核心角色。 对称性在物理学中的地位: 强大的自然定律往往根植于某种对称性。本书将详细讨论内禀对称性,特别是那些与规范场论紧密相关的对称群。我们将解释为什么 $SU(3) imes SU(2) imes U(1)$ 这样的数学结构,能够精确地描述我们观察到的所有基本相互作用(电磁力、弱核力和强核力)。读者将理解,这些对称性不仅仅是理论家的数学工具,它们是实验观测的必然结果,并且指导了对新粒子的预测。 量子场论的语言: 我们将介绍量子场论(QFT)作为描述粒子和相互作用的唯一有效语言。这并非是深入到复杂的正则化和重整化细节,而是侧重于理解QFT的基本哲学:粒子是场的激发态。我们会探讨如何用这种语言来描述粒子如何产生、湮灭以及相互转化,这些过程是所有高能物理实验的核心现象。 第二部分:力的本质——从宏观到微观的统一尝试 本书的第二部分聚焦于自然界的四种基本力,但视角将着重于它们在微观尺度上的唯象描述和统一前景。 电磁相互作用的量子描述: 量子电动力学(QED)是第一个成功的量子场论。我们将分析QED的核心概念,例如光子作为媒介粒子,以及拉格朗日量如何编码了电子和光子的相互作用。关键在于理解费曼图作为计算工具的意义,它们如何直观地表示了微观过程的概率振幅。 强相互作用的复杂性: 强力的描述是粒子物理学中最具挑战性的部分。本书将深入探讨量子色动力学(QCD)的特点,特别是渐近自由和夸克禁闭这两个看似矛盾的特性是如何并存于理论之中的。我们将讨论畴壁、真空结构等概念,它们是理解强子(如质子和中子)内部动态结构的关键。这种讨论将超越简单的夸克模型,触及到手征对称性的自发破缺等深层物理。 弱相互作用与规范理论的统一: 弱相互作用的描述,尤其是它能够改变粒子味(例如中微子的振荡),是电弱统一理论成功的基石。我们将详细讨论希格斯机制,它不仅仅是赋予粒子质量的“粘性”概念,更是规范对称性自发破缺的必然产物。读者将理解,电弱统一如何通过引入规范玻色子 $W^pm$ 和 $Z^0$ 来实现,以及这些玻色子质量的起源。 第三部分:超越标准模型——未解之谜与前沿探索 标准模型在描述已知的基本粒子和三种相互作用方面取得了空前的成功,但它并非终极理论。本书的最后部分将转向当前物理学家面临的重大挑战和潜在的新物理学领域。 引力问题的悬而未决: 最大的难题在于如何将引力(由广义相对论描述)纳入量子场论的框架。我们将探讨量子引力研究的困难所在,以及诸如弦理论或圈量子引力等尝试如何试图调和这两大支柱理论。本书将侧重于概念上的区别,例如时空在量子尺度上的离散化或涨落的可能性。 暗物质与暗能量的谜团: 观测证据明确指向宇宙中存在大量不与已知粒子相互作用的物质(暗物质)和驱动宇宙加速膨胀的能量(暗能量)。本书将详细分析目前主流的暗物质候选者(如WIMPs、轴子)的实验搜索策略,以及它们如何与粒子物理学标准模型相衔接或相悖。对于暗能量,我们将探讨其与真空能的联系,以及宇宙学常数问题所揭示的理论缺陷。 中微子物理学的革命: 中微子质量的发现(通过中微子振荡)已经确凿地证明标准模型是不完备的。我们将探讨这些发现对粒子物理学意味着什么——例如,它们可能暗示了西斯(See-Saw)机制或更高能级的新物理。 CP破坏与物质-反物质不对称性: 宇宙中物质远多于反物质,这要求CP对称性在早期宇宙中被破坏。本书将分析标准模型内CP破坏的来源(主要来自夸克扇区的卡比博-小林-高大(CKM)矩阵)及其不足,并探讨超越标准模型的新CP破坏机制,如在轻子扇区或希格斯扇区的可能性。 本书旨在培养读者一种结构化的、批判性的思维方式,使他们能够理解现代物理学是如何从数学对称性推导出物质的性质,并认识到目前理论框架的边界所在。重点在于构建对相互作用如何通过规范场传递的深刻理解,以及对实验观测如何驱动理论创新的深刻认识。