DOCSLIB.ORG

Fields and Vector Calculus the Electric Potential Is a Scalar field

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Fields and Vector Calculus the Electric Potential Is a Scalar field Fields and vector calculus The electric potential is a scalar field. The velocity of the air flow at any given point is a vector. These vectors will be different at different points, so they are functions of position (and also of time). Thus, the air velocity is a vector field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. For example: (a) Suppose we want to model the flow of air around an aeroplane. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. The electric potential is a scalar field. The velocity of the air flow at any given point is a vector. These vectors will be different at different points, so they are functions of position (and also of time). Thus, the air velocity is a vector field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. For example: (a) Suppose we want to model the flow of air around an aeroplane. The electric potential is a scalar field. These vectors will be different at different points, so they are functions of position (and also of time). Thus, the air velocity is a vector field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. For example: (a) Suppose we want to model the flow of air around an aeroplane. The velocity of the air flow at any given point is a vector. The electric potential is a scalar field. Thus, the air velocity is a vector field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. For example: (a) Suppose we want to model the flow of air around an aeroplane. The velocity of the air flow at any given point is a vector. These vectors will be different at different points, so they are functions of position (and also of time). The electric potential is a scalar field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. For example: (a) Suppose we want to model the flow of air around an aeroplane. The velocity of the air flow at any given point is a vector. These vectors will be different at different points, so they are functions of position (and also of time). Thus, the air velocity is a vector field. The electric potential is a scalar field. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. For example: (a) Suppose we want to model the flow of air around an aeroplane. The velocity of the air flow at any given point is a vector. These vectors will be different at different points, so they are functions of position (and also of time). Thus, the air velocity is a vector field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. The electric potential is a scalar field. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. For example: (a) Suppose we want to model the flow of air around an aeroplane. The velocity of the air flow at any given point is a vector. These vectors will be different at different points, so they are functions of position (and also of time). Thus, the air velocity is a vector field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. For example: (a) Suppose we want to model the flow of air around an aeroplane. The velocity of the air flow at any given point is a vector. These vectors will be different at different points, so they are functions of position (and also of time). Thus, the air velocity is a vector field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. The electric potential is a scalar field. Vector fields and scalar fields In many applications, we do not consider individual vectors or scalars, but functions that give a vector or scalar at every point. Such functions are called vector fields or scalar fields. For example: (a) Suppose we want to model the flow of air around an aeroplane. The velocity of the air flow at any given point is a vector. These vectors will be different at different points, so they are functions of position (and also of time). Thus, the air velocity is a vector field. Similarly, the pressure and temperature are scalar quantities that depend on position, or in other words, they are scalar fields. (b) The magnetic field inside an electrical machine is a vector that depends on position, or in other words a vector field. The electric potential is a scalar field. Although we will mainly be concerned with scalar and vector fields in three-dimensional space, we will sometimes use two-dimensional examples because they are easier to visualise. , and similarly for any other value of x. 2 I When (x; y) = (0; 0:4) we have u = ((1 − 0:4 )=5; 0) = (0:168; 0) I When (x; y) = (1:2; 0:4) we again have u = (0:168; 0) 2 I When y = 0:8 we have u = ((1 − 0:8 )=5; 0) = (0:072; 0) 2 I When y = −0:8 we have u = ((1 − (−0:8) )=5; 0) = (0:072; 0) The vector field u = ((1 − y 2)=5; 0) y=1 y=−1 , and similarly for any other value of x.
Load more

Recommended publications
  • An Introduction to Quantum Field Theory
    AN INTRODUCTION TO QUANTUM FIELD THEORY By Dr M Dasgupta University of Manchester Lecture presented at the School for Experimental High Energy Physics Students Somerville College, Oxford, September 2009 - 1 - - 2 - Contents 0 Prologue....................................................................................................... 5 1 Introduction ................................................................................................ 6 1.1 Lagrangian formalism in classical mechanics......................................... 6 1.2 Quantum mechanics................................................................................... 8 1.3 The Schrödinger picture........................................................................... 10 1.4 The Heisenberg picture............................................................................ 11 1.5 The quantum mechanical harmonic oscillator ..................................... 12 Problems .............................................................................................................. 13 2 Classical Field Theory............................................................................. 14 2.1 From N-point mechanics to field theory ............................................... 14 2.2 Relativistic field theory ............................................................................ 15 2.3 Action for a scalar field ............................................................................ 15 2.4 Plane wave solution to the Klein-Gordon equation ...........................
    [Show full text]
  • Exact Solutions to the Interacting Spinor and Scalar Field Equations in the Godel Universe
    XJ9700082 E2-96-367 A.Herrera 1, G.N.Shikin2 EXACT SOLUTIONS TO fHE INTERACTING SPINOR AND SCALAR FIELD EQUATIONS IN THE GODEL UNIVERSE 1 E-mail: [email protected] ^Department of Theoretical Physics, Russian Peoples ’ Friendship University, 117198, 6 Mikluho-Maklaya str., Moscow, Russia ^8 as ^; 1996 © (XrbCAHHeHHuft HHCTtrryr McpHMX HCCJicAOB&Htift, fly 6na, 1996 1. INTRODUCTION Recently an increasing interest was expressed to the search of soliton-like solu ­ tions because of the necessity to describe the elementary particles as extended objects [1]. In this work, the interacting spinor and scalar field system is considered in the external gravitational field of the Godel universe in order to study the influence of the global properties of space-time on the interaction of one ­ dimensional fields, in other words, to observe what is the role of gravitation in the interaction of elementary particles. The Godel universe exhibits a number of unusual properties associated with the rotation of the universe [2]. It is ho ­ mogeneous in space and time and is filled with a perfect fluid. The main role of rotation in this universe consists in the avoidance of the cosmological singu ­ larity in the early universe, when the centrifugate forces of rotation dominate over gravitation and the collapse does not occur [3]. The paper is organized as follows: in Sec. 2 the interacting spinor and scalar field system with £jnt = | <ptp<p'PF(Is) in the Godel universe is considered and exact solutions to the corresponding field equations are obtained. In Sec. 3 the properties of the energy density are investigated.
    [Show full text]
  • An Introduction to Supersymmetry
    An Introduction to Supersymmetry Ulrich Theis Institute for Theoretical Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, D–07743 Jena, Germany [email protected] This is a write-up of a series of five introductory lectures on global supersymmetry in four dimensions given at the 13th “Saalburg” Summer School 2007 in Wolfersdorf, Germany. Contents 1 Why supersymmetry? 1 2 Weyl spinors in D=4 4 3 The supersymmetry algebra 6 4 Supersymmetry multiplets 6 5 Superspace and superfields 9 6 Superspace integration 11 7 Chiral superfields 13 8 Supersymmetric gauge theories 17 9 Supersymmetry breaking 22 10 Perturbative non-renormalization theorems 26 A Sigma matrices 29 1 Why supersymmetry? When the Large Hadron Collider at CERN takes up operations soon, its main objective, besides confirming the existence of the Higgs boson, will be to discover new physics beyond the standard model of the strong and electroweak interactions. It is widely believed that what will be found is a (at energies accessible to the LHC softly broken) supersymmetric extension of the standard model. What makes supersymmetry such an attractive feature that the majority of the theoretical physics community is convinced of its existence? 1 First of all, under plausible assumptions on the properties of relativistic quantum field theories, supersymmetry is the unique extension of the algebra of Poincar´eand internal symmtries of the S-matrix. If new physics is based on such an extension, it must be supersymmetric. Furthermore, the quantum properties of supersymmetric theories are much better under control than in non-supersymmetric ones, thanks to powerful non- renormalization theorems.
    [Show full text]
  • Vector Fields
    Vector Calculus Independent Study Unit 5: Vector Fields A vector field is a function which associates a vector to every point in space. Vector fields are everywhere in nature, from the wind (which has a velocity vector at every point) to gravity (which, in the simplest interpretation, would exert a vector force at on a mass at every point) to the gradient of any scalar field (for example, the gradient of the temperature field assigns to each point a vector which says which direction to travel if you want to get hotter fastest). In this section, you will learn the following techniques and topics: • How to graph a vector field by picking lots of points, evaluating the field at those points, and then drawing the resulting vector with its tail at the point. • A flow line for a velocity vector field is a path ~σ(t) that satisfies ~σ0(t)=F~(~σ(t)) For example, a tiny speck of dust in the wind follows a flow line. If you have an acceleration vector field, a flow line path satisfies ~σ00(t)=F~(~σ(t)) [For example, a tiny comet being acted on by gravity.] • Any vector field F~ which is equal to ∇f for some f is called a con- servative vector field, and f its potential. The terminology comes from physics; by the fundamental theorem of calculus for work in- tegrals, the work done by moving from one point to another in a conservative vector field doesn’t depend on the path and is simply the difference in potential at the two points.
    [Show full text]
  • TASI 2008 Lectures: Introduction to Supersymmetry And
    TASI 2008 Lectures: Introduction to Supersymmetry and Supersymmetry Breaking Yuri Shirman Department of Physics and Astronomy University of California, Irvine, CA 92697. [email protected] Abstract These lectures, presented at TASI 08 school, provide an introduction to supersymmetry and supersymmetry breaking. We present basic formalism of supersymmetry, super- symmetric non-renormalization theorems, and summarize non-perturbative dynamics of supersymmetric QCD. We then turn to discussion of tree level, non-perturbative, and metastable supersymmetry breaking. We introduce Minimal Supersymmetric Standard Model and discuss soft parameters in the Lagrangian. Finally we discuss several mech- anisms for communicating the supersymmetry breaking between the hidden and visible sectors. arXiv:0907.0039v1 [hep-ph] 1 Jul 2009 Contents 1 Introduction 2 1.1 Motivation..................................... 2 1.2 Weylfermions................................... 4 1.3 Afirstlookatsupersymmetry . .. 5 2 Constructing supersymmetric Lagrangians 6 2.1 Wess-ZuminoModel ............................... 6 2.2 Superfieldformalism .............................. 8 2.3 VectorSuperfield ................................. 12 2.4 Supersymmetric U(1)gaugetheory ....................... 13 2.5 Non-abeliangaugetheory . .. 15 3 Non-renormalization theorems 16 3.1 R-symmetry.................................... 17 3.2 Superpotentialterms . .. .. .. 17 3.3 Gaugecouplingrenormalization . ..... 19 3.4 D-termrenormalization. ... 20 4 Non-perturbative dynamics in SUSY QCD 20 4.1 Affleck-Dine-Seiberg
    [Show full text]
  • SCALAR FIELDS Gradient of a Scalar Field F(X), a Vector Field: Directional
    53:244 (58:254) ENERGY PRINCIPLES IN STRUCTURAL MECHANICS SCALAR FIELDS Ø Gradient of a scalar field f(x), a vector field: ¶f Ñf( x ) = ei ¶xi Ø Directional derivative of f(x) in the direction s: Let u be a unit vector that defines the direction s: ¶x u = i e ¶s i Ø The directional derivative of f in the direction u is given as df = u · Ñf ds Ø The scalar component of Ñf in any direction gives the rate of change of df/ds in that direction. Ø Let q be the angle between u and Ñf. Then df = u · Ñf = u Ñf cos q = Ñf cos q ds Ø Therefore df/ds will be maximum when cosq = 1; i.e., q = 0. This means that u is in the direction of f(x). Ø Ñf points in the direction of the maximum rate of increase of the function f(x). Lecture #5 1 53:244 (58:254) ENERGY PRINCIPLES IN STRUCTURAL MECHANICS Ø The magnitude of Ñf equals the maximum rate of increase of f(x) per unit distance. Ø If direction u is taken as tangent to a f(x) = constant curve, then df/ds = 0 (because f(x) = c). df = 0 Þ u· Ñf = 0 Þ Ñf is normal to f(x) = c curve or surface. ds THEORY OF CONSERVATIVE FIELDS Vector Field Ø Rule that associates each point (xi) in the domain D (i.e., open and connected) with a vector F = Fxi(xj)ei; where xj = x1, x2, x3. The vector field F determines at each point in the region a direction.
    [Show full text]
  • 9.7. Gradient of a Scalar Field. Directional Derivatives. A. The
    9.7. Gradient of a Scalar Field. Directional Derivatives. A. The Gradient. 1. Let f: R3 ! R be a scalar ¯eld, that is, a function of three variables. The gradient of f, denoted rf, is the vector ¯eld given by " # @f @f @f @f @f @f rf = ; ; = i + j + k: @x @y @y @x @y @z 2. Symbolically, we can consider r to be a vector of di®erential operators, that is, @ @ @ r = i + j + k: @x @y @z Then rf is symbolically the \vector" r \times" the \scalar" f. 3. Note that rf is a vector ¯eld so that at each point P , rf(P ) is a vector, not a scalar. B. Directional Derivative. 1. Recall that for an ordinary function f(t), the derivative f 0(t) represents the rate of change of f at t and also the slope of the tangent line at t. The gradient provides an analogous quantity for scalar ¯elds. 2. When considering the rate of change of a scalar ¯eld f(x; y; z), we talk about its rate of change in a direction b. (So that b is a unit vector.) 3. The directional derivative of f at P in direction b is f(P + tb) ¡ f(P ) Dbf(P ) = lim = rf(P ) ¢ b: t!0 t Note that in this de¯nition, b is assumed to be a unit vector. C. Maximum Rate of Change. 1. The directional derivative satis¯es Dbf(P ) = rf(P ) ¢ b = jbjjrf(P )j cos γ = jrf(P )j cos γ where γ is the angle between b and rf(P ).
    [Show full text]
  • Introduction to Supersymmetry
    Introduction to Supersymmetry Pre-SUSY Summer School Corpus Christi, Texas May 15-18, 2019 Stephen P. Martin Northern Illinois University [email protected] 1 Topics: Why: Motivation for supersymmetry (SUSY) • What: SUSY Lagrangians, SUSY breaking and the Minimal • Supersymmetric Standard Model, superpartner decays Who: Sorry, not covered. • For some more details and a slightly better attempt at proper referencing: A supersymmetry primer, hep-ph/9709356, version 7, January 2016 • TASI 2011 lectures notes: two-component fermion notation and • supersymmetry, arXiv:1205.4076. If you find corrections, please do let me know! 2 Lecture 1: Motivation and Introduction to Supersymmetry Motivation: The Hierarchy Problem • Supermultiplets • Particle content of the Minimal Supersymmetric Standard Model • (MSSM) Need for “soft” breaking of supersymmetry • The Wess-Zumino Model • 3 People have cited many reasons why extensions of the Standard Model might involve supersymmetry (SUSY). Some of them are: A possible cold dark matter particle • A light Higgs boson, M = 125 GeV • h Unification of gauge couplings • Mathematical elegance, beauty • ⋆ “What does that even mean? No such thing!” – Some modern pundits ⋆ “We beg to differ.” – Einstein, Dirac, . However, for me, the single compelling reason is: The Hierarchy Problem • 4 An analogy: Coulomb self-energy correction to the electron’s mass A point-like electron would have an infinite classical electrostatic energy. Instead, suppose the electron is a solid sphere of uniform charge density and radius R. An undergraduate problem gives: 3e2 ∆ECoulomb = 20πǫ0R 2 Interpreting this as a correction ∆me = ∆ECoulomb/c to the electron mass: 15 0.86 10− meters m = m + (1 MeV/c2) × .
    [Show full text]
  • 3. Introducing Riemannian Geometry
    3. Introducing Riemannian Geometry We have yet to meet the star of the show. There is one object that we can place on a manifold whose importance dwarfs all others, at least when it comes to understanding gravity. This is the metric. The existence of a metric brings a whole host of new concepts to the table which, collectively, are called Riemannian geometry.Infact,strictlyspeakingwewillneeda slightly di↵erent kind of metric for our study of gravity, one which, like the Minkowski metric, has some strange minus signs. This is referred to as Lorentzian Geometry and a slightly better name for this section would be “Introducing Riemannian and Lorentzian Geometry”. However, for our immediate purposes the di↵erences are minor. The novelties of Lorentzian geometry will become more pronounced later in the course when we explore some of the physical consequences such as horizons. 3.1 The Metric In Section 1, we informally introduced the metric as a way to measure distances between points. It does, indeed, provide this service but it is not its initial purpose. Instead, the metric is an inner product on each vector space Tp(M). Definition:Ametric g is a (0, 2) tensor field that is: Symmetric: g(X, Y )=g(Y,X). • Non-Degenerate: If, for any p M, g(X, Y ) =0forallY T (M)thenX =0. • 2 p 2 p p With a choice of coordinates, we can write the metric as g = g (x) dxµ dx⌫ µ⌫ ⌦ The object g is often written as a line element ds2 and this expression is abbreviated as 2 µ ⌫ ds = gµ⌫(x) dx dx This is the form that we saw previously in (1.4).
    [Show full text]
  • On the Backreaction of Scalar and Spinor Quantum Fields in Curved Spacetimes
    On the Backreaction of Scalar and Spinor Quantum Fields in Curved Spacetimes Dissertation zur Erlangung des Doktorgrades des Department Physik der Universität Hamburg vorgelegt von Thomas-Paul Hack aus Timisoara Hamburg 2010 Gutachter der Dissertation: Prof. Dr. K. Fredenhagen Prof. Dr. V. Moretti Prof. Dr. R. M. Wald Gutachter der Disputation: Prof. Dr. K. Fredenhagen Prof. Dr. W. Buchmüller Datum der Disputation: Mittwoch, 19. Mai 2010 Vorsitzender des Prüfungsausschusses: Prof. Dr. J. Bartels Vorsitzender des Promotionsausschusses: Prof. Dr. J. Bartels Dekan der Fakultät für Mathematik, Informatik und Naturwissenschaften: Prof. Dr. H. Graener Zusammenfassung In der vorliegenden Arbeit werden zunächst einige Konstruktionen und Resultate in Quantenfeldtheorie auf gekrümmten Raumzeiten, die bisher nur für das Klein-Gordon Feld behandelt und erlangt worden sind, für Dirac Felder verallgemeinert. Es wird im Rahmen des algebraischen Zugangs die erweiterte Algebra der Observablen konstruiert, die insbesondere normalgeordnete Wickpolynome des Diracfeldes enthält. Anschließend wird ein ausgezeichnetes Element dieser erweiterten Algebra, der Energie-Impuls Tensor, analysiert. Unter Zuhilfenahme ausführlicher Berechnungen der Hadamardkoe ?zienten des Diracfeldes wird gezeigt, dass eine lokale, kovariante und kovariant erhaltene Konstruktion des Energie- Impuls Tensors möglich ist. Anschließend wird das Verhältnis der mathematisch fundierten Hadamardreg- ularisierung des Energie-Impuls Tensors mit der mathematisch weniger rigorosen DeWitt-Schwinger
    [Show full text]
  • Conformal Covariance and Invariant Formulation of Scalar Wave Equations Annales De L’I
    ANNALES DE L’I. H. P., SECTION A I. I. TUGOV Conformal covariance and invariant formulation of scalar wave equations Annales de l’I. H. P., section A, tome 11, no 2 (1969), p. 207-220 <http://www.numdam.org/item?id=AIHPA_1969__11_2_207_0> © Gauthier-Villars, 1969, tous droits réservés. L’accès aux archives de la revue « Annales de l’I. H. P., section A » implique l’accord avec les conditions générales d’utilisation (http://www.numdam. org/conditions). Toute utilisation commerciale ou impression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/ Ann. Inst. Henri Poincaré, Section A : Vol. XI, n° 2, 1969, 207 Physique théorique. Conformal covariance and invariant formulation of scalar wave equations I. I. TUGOV (P. N. Lebedev Physical Institute, Moscow, U. S. S. R.). ABSTRACT. - A new formulation of the scalar field equation or the Klein- Gordon equation in the presence of external tensor vector Ai(x) and scalar c(x) field is given, which is covariant with respect to gauge transfor- mations Ai(x) - A;(x) + V iV(X) and conformal transformations of the tensor field gi’(x) - exp [- 0(x)]g", v(x) and 8(x) are arbitrary functions of x = (xl, x2, ... , x"). In this case the rest mass square m2(x) defined as the function of given fields rn2 x - c 2014 .-20142014-. R - 1 V iAi, transforms as follows : m2(x) - exp [- 0(:B’)]~(jc).
    [Show full text]
  • Introduction to Supersymmetry
    Introduction to Supersymmetry J.W. van Holten NIKHEF Amsterdam NL 1 Relativistic particles a. Energy and momentum The energy and momentum of relativistic particles are related by E2 = p2c2 + m2c4: (1) In covariant notation we define the momentum four-vector E E pµ = (p0; p) = ; p ; p = (p ; p) = − ; p : (2) c µ 0 c The energy-momentum relation (1) can be written as µ 2 2 p pµ + m c = 0; (3) where we have used the Einstein summation convention, which implies automatic summa- tion over repeated indices like µ. Particles can have different masses, spins and charges (electric, color, flavor, ...). The differences are reflected in the various types of fields used to describe the quantum states of the particles. To guarantee the correct energy-momentum relation (1), any free field Φ must satisfy the Klein-Gordon equation 2 − 2@µ@ + m2c2 Φ = ~ @2 − 2r2 + m2c2 Φ = 0: (4) ~ µ c2 t ~ Indeed, a plane wave Φ = φ(k) ei(k·x−!t); (5) satisfies the Klein-Gordon equation if E = ~!; p = ~k: (6) From now on we will use natural units in which ~ = c = 1. In these units we can write the plane-wave fields (5) as Φ = φ(p) eip·x = φ(p) ei(p·x−Et): (7) b. Spin Spin is the intrinsic angular momentum of particles. The word `intrinsic' is to be inter- preted somewhat differently for massive and massless particles. For massive particles it is the angular momentum in the rest-frame of the particles, whilst for massless particles {for which no rest-frame exists{ it is the angular momentum w.r.t.
    [Show full text]