# The Dirac Equation May 18, 2015

Save this PDF as:

Size: px
Start display at page:

## Transcription

1 The Dirac Equation May 8, 25

2 . Introduction In non-relativistic quantum mechanics, wave functions are descibed by the time-dependent Schrodinger equation : 2m 2 ψ + V ψ = i () This is really just energy conservation ( kinetic energy ( p2 ) plus potential energy (V) equals total 2m energy (E)) with the momentum and energy terms replaced by their operator equivalents p i ; E i (2) In relativistic quantum theory, the energy-momentum conservation equation is E 2 p 2 = m 2 (note that we are working in the standard particle physics units where h = c = ). Proceeding with the same replacements, we can derive the Klein-Gordon equation : In covariant notation this is E 2 p 2 m 2 2 ψ ψ m 2 = (3) µ µ ψ m 2 ψ = (4) Suppose ψ is solution to the Klein-Gordon equation. Multiplying it by iψ we get iψ 2 ψ 2 iψ 2 ψ + iψ m 2 = (5) Taking the complex conjugate of the Klein-Gordon equation and multiplying by iψ we get iψ 2 ψ 2 iψ 2 ψ + iψm 2 = (6) If we subtract the second from the first we obtain [ ( i ψ )] ψ + [ i (ψ ψ ψ ψ )] = (7) This has the form of an equation of continuity with a probability density defined by ρ + j = (8) ( ρ = i ψ ) ψ (9) and a probability density current defined by j = i (ψ ψ ψ ψ ) () Now, suppose a solution to the Klein-Gordon equation is a free particle with energy E and momentum p ψ = Ne ipµxµ ()

3 Substitution of this solution into the equation for the probability density yields ρ = 2E N 2 (2) The probability density is proportional to the energy of the particle. Now, why is this a problem? If you substitute the free particle solution into the Klein-Gordon equation you get, unsurpisingly, the relation E 2 p 2 = m 2 (3) so the energy of the particle could be E = ± p 2 + m 2 (4) The fact that you have negative energy solutions is not that much of a problem. What is a problem is that the probability density is proportional to E. This implies a possibility for negative probability densities...which don t exist. This (and some others) problem drove Dirac to think about another equation of motion. His starting point was to try to factorise the energy momentum relation. In covariant formalism where p µ is the 4-momentum : (E, p x, p y, p z ). Dirac tried to write E 2 p 2 m 2 p µ p µ m 2 (5) p µ p µ m 2 = (β κ p κ + m)(γ λ p λ m) (6) where κ and λ range from to 3. This notation looks a bit confusing. It may help if we write both sides out long-hand. On the left-hand side we have On the right-hand side we have p µ p µ m 2 = p 2 p p = p 2 p 2 p 2 2 p 2 3 m 2 (7) (β κ p κ + m)(γ λ p λ m) = (β p β p β 2 p 2 β 3 p 3 + m)(γ p γ p γ 2 p 2 γ 3 p 3 m) (8) Expanding the right-hand side (β κ p κ + m)(γ λ p λ m) = β κ γ λ p κ p λ m 2 + mγ λ p λ mβ κ p κ (9) This should be equal to p µ p µ m 2, so we need to get rid of the terms that are linear in p. We can do this just be choosing β κ = γ κ. Then p µ p µ m 2 = γ κ γ λ p κ p λ m 2 (2) Now, since κ, λ runs from to 3, the right hand side can be fully expressed by γ κ γ λ p κ p λ m 2 = (γ ) 2 p 2 + (γ ) 2 p 2 + (γ 2 ) 2 p (γ 3 ) 2 p 2 3 (2) + (γ γ + γ γ )p p + (γ γ 2 + γ 2 γ )p p 2 (22) + (γ γ 3 + γ 3 γ )p p 3 + (γ γ 2 + γ 2 γ )p p 2 (23) + (γ γ 3 + γ 3 γ )p p 3 + (γ 2 γ 3 + γ 3 γ 2 )p 2 p 3 m 2 (24) 2

4 This must be equal to p µ p µ m 2 = p 2 p 2 p 2 2 p 2 3 m 2 (25) One could make the squared terms equal by choosing (γ ) 2 = and (γ ) 2 = (γ 2 ) 2 = (γ 3 ) 2 =-, but this would not eliminate the cross-terms. Dirac realised that what you needed was something which anticommuted : i.e. γ µ γ ν + γ ν γ µ = if µ ν. He realised that the γ factors must be 4x4 matrices, not just numbers, which satisfied the anticommutation relation where {γ µ, γ ν } = 2g µν (26) g µν = (27) We also define, for later use, another γ matrix called γ 5 = iγ γ γ 2 γ 3. This has the properties (you should check for yourself) that (γ 5 ) 2 =, {γ 5, γ µ } = (28) We will want to take the Hermitian conjugate of these matrices at various times. The Hermitian conjugate of each matrix is γ = γ γ 5 = γ 5 γ µ = γ γ µ γ = γ for µ (29) If the matrices satisfy this algebra, then you can factor the energy momentum conservation equation p µ p µ m 2 = (γ κ p κ + m)(γ λ p λ m) = (3) The Dirac equation is one of the two factors, and is conventionally taken to be Making the standard substitution, p µ equation γ λ p λ m = (3) i µ we then have the usual covariant form of the Dirac (iγ µ µ m)ψ = (32) where µ = (,,, ), m is the particle mass and the γ matrices are a set of 4-dimensional x y z matrices. Since these are matrices, ψ is a 4-element column matrix called a bi-spinor. This bi-spinor is not a 4-vector and doesn t transform like one..2 The Bjorken-Drell convention Any set of four 4x4 matrices that obey the algebra above will work. The one we normally use includes the Pauli spin matrices. Recall that each component of the spin operator S for spin /2 particles is defined by its own Pauli spin matrix : S x = 2 σ = 2 ( ) S y = 2 σ 2 = 2 3 ( ) i i S z = 2 σ 3 = 2 ( ) (33)

5 In terms of the Pauli spin matrices, the γ matrices have the form ( ) ( ) σ γ = γ µ µ = σ µ γ 5 = ( ) Each element of the matrices in Equations 34 are 2x2 matrices. denotes the 2 x 2 unit matrix, and denotes the 2 x 2 null matrix..3 The Probability Density and Current In order to understand the probability density and probability flow we will want to derive an equation of continuity for the probability. The first step is to write the Dirac equation out longhand : iγ + iγ x + iγ2 y We want to take the Hermitian conjugate of this : [iγ + iγ x + iγ2 y + iγ3 z (34) mψ = (35) + iγ3 z mψ] (36) Now, we must remember that the γ are matrices and that ψ is a 4-component column vector. Thus [γ ] = [ 2 3 ] (37) 4 2 = 3 (38) 4 ( ) = (39) = γ (4) Using the Hermitian conjugation properties of the γ matrices defined in the previous section we can write Equation 36 as i γ i x γ i y γ2 i z γ3 mψ (4) which, as γ µ = γ µ for µ means we can write this as i γ i x ( γ ) i y ( γ2 ) i z ( γ3 ) mψ (42) 4

6 We have a problem now - this is no longer covariant. That is, I would like to write this in the form ψ ( i µ γ µ m) where the derivative µ now operates to the left. I can t because the minus signs on the spatial components coming from the γ µ spoils the scalar product. To deal with this we have to multiply the equation on the right by γ, since we can flip the sign of the γ matrices using the relationship γ µ γ = γ γ µ. Thus or i γ γ i x ( γ γ ) i y ( γ2 γ ) i z ( γ3 γ ) mψ γ (43) i γ γ i x (γ γ ) i y (γ γ 2 ) i z (γ γ 3 ) mψ γ (44) Defining the adjoint spinor ψ = ψ γ, we can rewrite this equation as and finally we get the adjoint Dirac equation i γ i x (γ ) i y (γ2 ) i z (γ3 ) mψ (45) Now, we multiply the Dirac equation on the left by ψ : and the adjoint Dirac equation on the right by ψ : and we add them together, which eliminates the two mass terms or, more succinctly,. If we now identify the bit in the brackets as the 4-current : ψ(i µ γ µ + m) = (46) ψ(iγ µ µ m)ψ = (47) ψ(i µ γ µ + m)ψ = (48) ψ(γ µ µ ψ) + (ψ µ γ µ )ψ = (49) µ (ψγ µ ψ) = (5) j µ = (ρ, j) (5) where ρ is the probability density and j is the probability current, we can write the conservation equation as µ j µ = with j µ = ψγ µ ψ (52) which is the covariant form for an equation of continuity. The probability density is then just ρ = ψγ ψ = ψ γ γ ψ = ψ ψ and the probability 3-current is j = ψ γ γ µ ψ. This current is the same one which appears in the Feynman diagrams. It is called a Vector current, and is the current responsible for the electromagnetic interaction. 5

7 ψ i e ψ f e q γ e e φ i φ f For the interaction in Figure.3, with two electromagnetic interactions, the matrix element is then.4 Examples M = e2 4π [ψ fγ µ ψ i ] q 2 [φ fγ ν φ i ] (53) Now let s look at some solutions to the Dirac Equation. The first one we will look at is for a particle at rest..4. Particle at rest Suppose the fermion wavefunction is a plane wave. We can write this as ψ(p) = e ixµpµ u(p) (54) where p µ = (E, p x, p y, p z ) and x µ = (t, x, y, z) and so ix µ p µ = i(et x p). This is just the phase for an oscillating plane wave. For a particle at rest, the momentum term disappears : ix µ p µ = i(et). Furthur, since the momentum is zero, the spatial derivatives must be zero : reads x,y,z =. The Dirac equation therefore or which gives us iγ mψ = (55) iγ ( ie)u(p) mu(p) = (56) Eγ u(p) = mu(p) (57) 6

8 Now, u(p) is a 4-component bispinor, so properly expanding the gamma matrix in Equation 57, we get u E = m u 2 u 3 (58) u 4 This is an eigenvalue equation. There are four independent solutions. Two with energy E = m and two with E = m. The solutions are just u = u 2 = u 3 = u 4 = (59) with eigenvalues m, m, -m and -m respectively. The first two solutions can be interpreted as positive energy particle solutions with spin up and spin down. One can see this be checking if the function is an eigenfunction of the spin matrix : S z. S z u = 2 = 2 u (6) and similarly for u 2. Note that we have yet to normalise these solutions. We won t either for the purposes of this discussion. What about these negative energy solutions? We are required to keep them (we can t just say that they are unphysical and throw them away) since quantum mechanics requires a complete set of states. What happens if we allow the particle to have momentum?.4.2 Particle in Motion Again, let s look for a plane wave solution ψ(p) = e ixµpµ u(p) (6) Plugging this into the Dirac equation means that we can replace the µ by p µ and remove the oscillatory term to obtain the momentum-space version of the Dirac Equation (γ µ p µ m)u(p) = (62) Notice that this is now purely algebraic and can be easily(!) solved γ µ p µ m = Eγ p x γ p y γ 2 p z γ 3 m (63) ( ) ( ) ( ) σ = E p m (64) σ ( ) (E m) σ p = (65) σ p (E + m) 7

9 where each element in this 2x2 matrix is actually a 2x2 matrix itself. In this spirit, let s write the 4-component bispinor solution as 2-component vector ( ) ua u = (66) u B then the Dirac Equation implies that (γ µ p µ m)u(p) = = leading two coupled simultaneous equations ( ) ( ) (E m) σ p ua = σ p (E + m) u B ( ) (67) (σ p)u B = (E m)u A (68) (σ p)u A = (E + m)u B (69) Now, let s expand that (σ p) : (σ p) = = and right back to the Dirac Equation ( ) ( ) p x + p i y + ( ) pz p x ip y p x + ip y p z ( ) (7) (7) (σ p)u B = (E m)u A (72) (σ p)u A = (E + m)u B (73) gives u B = = (σ p) E + m u A (74) ( ) pz p x ip y u E + m p x + ip y p A (75) z Now, we just need to make choices for the form of u A. Let s make the obvious choice and remember that u A is a 2-component spinor so we need to specify two solutions: ( ) ( ) u A = or u A = (76) These give u = N p z p x+ip y and u 2 = N 2 p x ip y p z (77) where N and N 2 are normalisation factors we won t go into. Note that, if p = these correspond to the E > solutions we found for a particle at rest, which is good. 8

10 Repeating this for u B = ( ) and u B = u 3 = N 3 p z p x+ip y ( ) which gives solutions u 3 and u 4 p x ip y and u p z 4 = N 4 (78) and collecting them together u = N p z p x+ip y u 2 = N 2 p x ip y p z u 3 = N 3 p z p x+ip y u 4 = N 4 p x ip y p z (79) All of which, if put back into the Dirac Equation, yields : E 2 = p 2 + m 2 as you might expect. Comparing with the p = case we can identify u and u 2 as positive energy solutions with energy E = p 2 + m 2, and u 3, u 4 as negative energy solutions with energy E = p 2 + m 2. How do we interpret these negative energy solutions? The conventional interpretation is called the Feynman-Stuckelberg interpretation : A negative energy solution represents a negative energy particle travelling backwards in time, or equivalently, a positive energy antiparticle going forwards in time. With this interpretation we tend to rewrite the negative energy solutions to represent positive antiparticles. Starting from the E < solutions p z p x ip y p x+ip y u 3 = N 3 and u p z 4 = N 4 (8) Here we implicitly assume that E is negative. We define antiparticle states by just flipping the sign of E and p following the Feynman-Stuckelberg convention. v (E, p)e i(et x p) = u 4 ( E, p)e i(et x p) (8) v 2 (E, p)e i(et x p) = u 3 ( E, p)e i(et x p) (82) where E = p 2 + m 2. Note that v is associated with u 4 and v 2 is associated with u 3. We do this because the spin matrix, S antiparticle, for anti-particles is equal to S particle i.e. the spin flips for antiparticles as well and the spin eigenvalue for v = u 4 is spin-up and v 2 = u 3 is spin-down. In general u, u 2, v and v 2 are not eigenstates of the spin operator (Check for yourself). In fact we should expect this since solutions to the Dirac Equation are, by definition, eigenstates of the Hamiltonian operator, Ĥ, and the S z does not commute with the Hamiltonian : [Ĥ, Ŝz], and hence we can t find solutions which are simultaneously solutions to S z and Ĥ. However if the z-axis is aligned with particle direction : p x = p y =, p z = ± p then we have the following Dirac states u = N ± p u 2 = N p v = N 9 p ± p v 2 = N (83)

11 These are eigenstates of S z S z u = + 2 u S z u 2 = 2 u 2 S anti z v = S z v = + 2 v (84) S anti z v 2 = S z v 2 = 2 v 2 (85) So we have found solutions of the Dirac Equation which are also spin eigenstates...but only if the particle is travelling along the z-axis..4.3 Charge Conjugation Classical electrodynamics is invariant under a change in the sign of the electric charge. In particle physics, this concept is represented by the charge conjugation operator that flips the signs of all the charges. It changes a particle into an anti-particle, and vice versa: Ĉ p >= p > (86). Application of Ĉ twice brings us back to the the orignal state : Ĉ2 = and so eigenstates of Ĉ are ±. In general most particles are not eigenstates of Ĉ. If p > were an eigenstate of Ĉ then Ĉ p >= ± p >= p > (87) implying that only those particles which are their own antiparticles are eigenstates of Ĉ. This leaves us with photons and the neutral mesons like π, η and ρ. Ĉ changes a particle spinor into an anti-particle spinor. The relevant operation is ψ ψ C = Ĉγ ψ (88) with Ĉ = iγ2 γ. We can apply this to, say, the u solution to the Dirac Equation. if ψ = u e i(et x p), the ψ C = iγ 2 ψ = iγ 2 u e i(et x p) i iγ 2 u = i i i N i p z p x+ip y = N p x ip y p z = v (89) or, in full, Ĉ(u e i(et x p) ) = v e i(et x p). Hence charge conjugation changes the particle eigenspinors into their respective anti-particle spinors..4.4 Helicity The fact that we can find spin eigenvalues for states in which the particles are travelling along the spin-direction indicates that the quantity we need is not spin but helicity. The helicity is defined as the projection of the spin along the direction of motion: ( ) σ ĥ = Σ ˆp = 2S ˆp = ˆp (9) σ

12 Figure : The two helicity states. On the left the spin vector is aligned in the direction of motions of the particle. This is a right-handed helicity state and has helicity +. On the right the spin vector is antiparallel to the particle momentum. This is a left-handed helicity state with helicity -. and has eigenvalues equal to + (called right-handed where the spin vector is aligned in the same direction as the momentum vector) or - (called left-handed where the spin vector is aligned in the opposite direction as the momentum vector), corresponding to the diagrams in Figure. It can be shown that the helicity does commute with the Hamiltonian and so one can find eigenstates that are simultaneously states of helicity and the Hamiltonian. The problem, and it is a big problem, is that helicity is not Lorentz invariant in the case of a massive particle. If the particle is massive it is possible to find an inertial reference frame in which the particle is going in the opposite direction. This does not change the direction of the spin vector, so the helicity can change sign. The helicity is Lorentz invariant only in the case of massless particles..4.5 Chirality We d rather have operators which are Lorentz invariant, than commute with the Hamiltonian. In general wave functions in the Standard Model are eigenstates of a Lorentz invariant quantity called the chirality. The chirality operator is γ 5 and it does not commute with the Hamiltonian. Due to this, it is somewhat difficult to visualise. The best picture I can get comes from the definition : something is chiral if it s mirror image does not superimpose on itself. Think of your left hand. It s mirror image (from the point of view of someone in that mirror looking back at you) is actually a right hand. It and it s mirror image cannot be superimposed andit is therefore an intrinsically chiral object. In the limit that E >> m, or that the particle is massless, the chirality is identical to the helicity. For a massive particle this is no longer true. In general the eigenstates of the chirality operator are γ 5 u R = +u R γ 5 u L = u L γ 5 v R = v R γ 5 v L = +v L (9), where we define u R and u L are right- and left-handed chiral states. We can define the projection operators P L = 2 ( γ5 ) P R = 2 ( + γ5 ) (92) such that P L projects outs the left-handed chiral particle states and right-handed chiral anti-particle states. P R projects out the right-handed chiral particle states and left-handed chiral anti-particle states. The projection operators have the following properties : P 2 L,R = P L,R ; P R P L = P L P R = ; P R + P L = (93)

13 Any spinor can be written in terms of it s left- and right-handed chiral states: ψ = (P R + P L )ψ = P R ψ + P L ψ = ψ R + ψ L (94) Chirality holds an important place in the standard model. Let s take a standard model probability current ψγ µ φ (95) We can decompose this into it s chiral states ψγ µ φ = (ψ L + ψ R )γ µ (φ L + φ R ) = ψ L γ µ φ L + ψ L γ µ φ R + ψ R γ µ φ L + ψ R γ µ φ R Now, ψ L = ψ L γ = ψ 2 ( γ5 )γ = ψ γ 2 ( + γ5 ) = ψ 2 ( + γ5 ) = ψp R where I have used the fact that γ 5 = γ 5 and γ 5 γ = γ γ 5. Similarly ψ R = ψp L. Using this, it is easy to show that the terms ψ L γ µ φ R and ψ R γ µ φ L are equal to : ψ L γ µ φ R = ψp R γ µ P R φ (96) = ψ 2 ( + γ5 )γ µ 2 ( + γ5 )φ (97) = ψ 4 ( + γ5 )(γ µ + γ µ γ 5 )φ (98) = ψ 4 ( + γ5 )(γ µ γ 5 γ µ )φ (99) = ψ 4 ( + γ5 )( γ 5 )γ µ φ () = ψ 4 ( + γ5 γ 5 (γ 5 ) 2 )γ µ φ () = (2) since (γ 5 ) 2 = and γ µ γ 5 = γ 5 γ µ. Similarly for the other cross term, ψ R γ µ φ L. Hence, ψγ µ φ = ψ L γ µ φ L + ψ R γ µ φ R (3) So left-handed chiral particles couple only to left-handed chiral fields, and right-handed chiral fields couple to right-handed chiral fields. One must be very careful with how one interprets this statement. What it does not say is that there are left-handed chiral electrons and right-handed chiral electrons which are distinct particles. Useful though it is when describing particle interactions, chirality is not conserved in the propagation of a free particle. In fact the chiral states φ L and φ R do not even satisfy the Dirac equation. Since chirality is not a good quantum number it can evolve with time. A massive particle starting off as a completely left handed chiral state will soon evolve a right-handed chiral component. By contrast, helicity is a conserved quantity during free particle propagation. Only in the case of massless particles, for which helicity and chirality are identical and are conserved in free-particle propagation, can leftand right-handed particles be considered distinct. For neutrinos this mostly holds. 2

14 .5 What you should know Understand the covariant form of the Dirac equation, and know how to manipulate the γ matrices. Know where the definition of a current comes from. Understand the difference between helicity and chirality. Be able to manipulate gamma matrices..6 Futhur reading Griffiths Chapter 7, Sections 7., 7.2 and 7.3 Griffiths Chapter, Section.7 3

### We can represent the eigenstates for angular momentum of a spin-1/2 particle along each of the three spatial axes with column vectors: 1 +y =

Chapter 0 Pauli Spin Matrices We can represent the eigenstates for angular momentum of a spin-/ particle along each of the three spatial axes with column vectors: +z z [ ] 0 [ ] 0 +y y [ ] / i/ [ ] i/

### 1D 3D 1D 3D. is called eigenstate or state function. When an operator act on a state, it can be written as

Chapter 3 (Lecture 4-5) Postulates of Quantum Mechanics Now we turn to an application of the preceding material, and move into the foundations of quantum mechanics. Quantum mechanics is based on a series

### Mixed states and pure states

Mixed states and pure states (Dated: April 9, 2009) These are brief notes on the abstract formalism of quantum mechanics. They will introduce the concepts of pure and mixed quantum states. Some statements

### H = = + H (2) And thus these elements are zero. Now we can try to do the same for time reversal. Remember the

1 INTRODUCTION 1 1. Introduction In the discussion of random matrix theory and information theory, we basically explained the statistical aspect of ensembles of random matrices, The minimal information

### Chapter 22 The Hamiltonian and Lagrangian densities. from my book: Understanding Relativistic Quantum Field Theory. Hans de Vries

Chapter 22 The Hamiltonian and Lagrangian densities from my book: Understanding Relativistic Quantum Field Theory Hans de Vries January 2, 2009 2 Chapter Contents 22 The Hamiltonian and Lagrangian densities

### From Einstein to Klein-Gordon Quantum Mechanics and Relativity

From Einstein to Klein-Gordon Quantum Mechanics and Relativity Aline Ribeiro Department of Mathematics University of Toronto March 24, 2002 Abstract We study the development from Einstein s relativistic

### Subatomic Physics: Particle Physics Lecture 4. Quantum Electro-Dynamics & Feynman Diagrams. Antimatter. Virtual Particles. Yukawa Potential for QED

Ψ e (r, t) exp i/ (E)(t) (p) (r) Subatomic Physics: Particle Physics Lecture Quantum ElectroDynamics & Feynman Diagrams Antimatter Feynman Diagram and Feynman Rules Quantum description of electromagnetism

### Harmonic Oscillator Physics

Physics 34 Lecture 9 Harmonic Oscillator Physics Lecture 9 Physics 34 Quantum Mechanics I Friday, February th, 00 For the harmonic oscillator potential in the time-independent Schrödinger equation: d ψx

### Particle Physics. Michaelmas Term 2011 Prof Mark Thomson. Handout 7 : Symmetries and the Quark Model. Introduction/Aims

Particle Physics Michaelmas Term 2011 Prof Mark Thomson Handout 7 : Symmetries and the Quark Model Prof. M.A. Thomson Michaelmas 2011 206 Introduction/Aims Symmetries play a central role in particle physics;

### The Schrödinger Equation

The Schrödinger Equation When we talked about the axioms of quantum mechanics, we gave a reduced list. We did not talk about how to determine the eigenfunctions for a given situation, or the time development

### The Essentials of Quantum Mechanics

The Essentials of Quantum Mechanics Prof. Mark Alford v7, 2008-Oct-22 In classical mechanics, a particle has an exact, sharply defined position and an exact, sharply defined momentum at all times. Quantum

### Lecture 2. Observables

Lecture 2 Observables 13 14 LECTURE 2. OBSERVABLES 2.1 Observing observables We have seen at the end of the previous lecture that each dynamical variable is associated to a linear operator Ô, and its expectation

### Special Relativity and Electromagnetism Yannis PAPAPHILIPPOU CERN

Special Relativity and Electromagnetism Yannis PAPAPHILIPPOU CERN United States Particle Accelerator School, University of California - Santa Cruz, Santa Rosa, CA 14 th 18 th January 2008 1 Outline Notions

### 1 Spherical Kinematics

ME 115(a): Notes on Rotations 1 Spherical Kinematics Motions of a 3-dimensional rigid body where one point of the body remains fixed are termed spherical motions. A spherical displacement is a rigid body

### 07. Quantum Mechanics Basics.

07. Quantum Mechanics Basics. Stern-Gerlach Experiment (Stern & Gerlach 1922) magnets splotches sliver atoms detection screen Suggests: Electrons possess 2-valued "spin" properties. (Goudsmit & Uhlenbeck

### Quantum Mechanics I: Basic Principles

Quantum Mechanics I: Basic Principles Michael A. Nielsen University of Queensland I ain t no physicist but I know what matters - Popeye the Sailor Goal of this and the next lecture: to introduce all the

### Contents Quantum states and observables

Contents 2 Quantum states and observables 3 2.1 Quantum states of spin-1/2 particles................ 3 2.1.1 State vectors of spin degrees of freedom.......... 3 2.1.2 Pauli operators........................

### Feynman diagrams. 1 Aim of the game 2

Feynman diagrams Contents 1 Aim of the game 2 2 Rules 2 2.1 Vertices................................ 3 2.2 Anti-particles............................. 3 2.3 Distinct diagrams...........................

### 1. The quantum mechanical state of a hydrogen atom is described by the following superposition: ψ = (2ψ 1,0,0 3ψ 2,0,0 ψ 3,2,2 )

CHEM 352: Examples for chapter 2. 1. The quantum mechanical state of a hydrogen atom is described by the following superposition: ψ = 1 14 2ψ 1,, 3ψ 2,, ψ 3,2,2 ) where ψ n,l,m are eigenfunctions of the

### For the case of an N-dimensional spinor the vector α is associated to the onedimensional . N

1 CHAPTER 1 Review of basic Quantum Mechanics concepts Introduction. Hermitian operators. Physical meaning of the eigenvectors and eigenvalues of Hermitian operators. Representations and their use. on-hermitian

### Introduction to SME and Scattering Theory. Don Colladay. New College of Florida Sarasota, FL, 34243, U.S.A.

June 2012 Introduction to SME and Scattering Theory Don Colladay New College of Florida Sarasota, FL, 34243, U.S.A. This lecture was given at the IUCSS summer school during June of 2012. It contains a

### UNIT 2 MATRICES - I 2.0 INTRODUCTION. Structure

UNIT 2 MATRICES - I Matrices - I Structure 2.0 Introduction 2.1 Objectives 2.2 Matrices 2.3 Operation on Matrices 2.4 Invertible Matrices 2.5 Systems of Linear Equations 2.6 Answers to Check Your Progress

### 2. Introduction to quantum mechanics

2. Introduction to quantum mechanics 2.1 Linear algebra Dirac notation Complex conjugate Vector/ket Dual vector/bra Inner product/bracket Tensor product Complex conj. matrix Transpose of matrix Hermitian

### The Quantum Harmonic Oscillator Stephen Webb

The Quantum Harmonic Oscillator Stephen Webb The Importance of the Harmonic Oscillator The quantum harmonic oscillator holds a unique importance in quantum mechanics, as it is both one of the few problems

### 6. Quantum Electrodynamics

6. Quantum Electrodynamics In this section we finally get to quantum electrodynamics QED), the theory of light interacting with charged matter. Our path to quantization will be as before: we start with

### PHY411. PROBLEM SET 3

PHY411. PROBLEM SET 3 1. Conserved Quantities; the Runge-Lenz Vector The Hamiltonian for the Kepler system is H(r, p) = p2 2 GM r where p is momentum, L is angular momentum per unit mass, and r is the

### Lecture 4. Reading: Notes and Brennan

Lecture 4 Postulates of Quantum Mechanics, Operators and Mathematical Basics of Quantum Mechanics Reading: Notes and Brennan.3-.6 ECE 645 - Dr. Alan Doolittle Postulates of Quantum Mechanics Classical

### Quanta of Geometry and Unification

Quanta of Geometry and Unification Memorial Meeting for Abdus Salam 90 th Birthday Ali Chamseddine American University of Beirut (AUB) and Institut des Hautes Etudes Scientifique (IHES) January 25-28,

### The Central Equation

The Central Equation Mervyn Roy May 6, 015 1 Derivation of the central equation The single particle Schrödinger equation is, ( H E nk ψ nk = 0, ) ( + v s(r) E nk ψ nk = 0. (1) We can solve Eq. (1) at given

### Lecture-XXIV. Quantum Mechanics Expectation values and uncertainty

Lecture-XXIV Quantum Mechanics Expectation values and uncertainty Expectation values We are looking for expectation values of position and momentum knowing the state of the particle, i,e., the wave function

### Gauge Field Theory UNIVERSITY OF CAMBRIDGE PART III NATURAL SCIENCES TRIPOS. Dr. Ben Gripaios.

UNIVERSITY OF CAMBRIDGE PART III NATURAL SCIENCES TRIPOS Gauge Field Theory Dr. Ben Gripaios Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, United Kingdom. January 4, 2016 E-mail: gripaios@hep.phy.cam.ac.uk

### 1. Coordinates (x, t) in one frame are related to coordinates (x, t ) in another frame by the Lorentz transformation formulas.

Physics 00 Problem Set 7 Solution Quick overview: Although relativity can be a little bewildering, this problem set uses just a few ideas over and over again, namely. Coordinates x, t in one frame are

### Time Ordered Perturbation Theory

Michael Dine Department of Physics University of California, Santa Cruz October 2013 Quantization of the Free Electromagnetic Field We have so far quantized the free scalar field and the free Dirac field.

### 2x + y = 3. Since the second equation is precisely the same as the first equation, it is enough to find x and y satisfying the system

1. Systems of linear equations We are interested in the solutions to systems of linear equations. A linear equation is of the form 3x 5y + 2z + w = 3. The key thing is that we don t multiply the variables

### Helpsheet. Giblin Eunson Library MATRIX ALGEBRA. library.unimelb.edu.au/libraries/bee. Use this sheet to help you:

Helpsheet Giblin Eunson Library ATRIX ALGEBRA Use this sheet to help you: Understand the basic concepts and definitions of matrix algebra Express a set of linear equations in matrix notation Evaluate determinants

### The basic unit in matrix algebra is a matrix, generally expressed as: a 11 a 12. a 13 A = a 21 a 22 a 23

(copyright by Scott M Lynch, February 2003) Brief Matrix Algebra Review (Soc 504) Matrix algebra is a form of mathematics that allows compact notation for, and mathematical manipulation of, high-dimensional

### Quantum Mechanics: Fundamental Principles and Applications

Quantum Mechanics: Fundamental Principles and Applications John F. Dawson Department of Physics, University of New Hampshire, Durham, NH 0384 October 14, 009, 9:08am EST c 007 John F. Dawson, all rights

### Chapter 3. Principles and Spin. There are many axiomatic presentations of quantum mechanics that aim at

Chapter 3 Principles and Spin 3. Four Principles of Quantum Mechanics There are many axiomatic presentations of quantum mechanics that aim at conceptual economy and rigor. However, it would be unwise for

### Definition 12 An alternating bilinear form on a vector space V is a map B : V V F such that

4 Exterior algebra 4.1 Lines and 2-vectors The time has come now to develop some new linear algebra in order to handle the space of lines in a projective space P (V ). In the projective plane we have seen

### Laws of Motion and Conservation Laws

Laws of Motion and Conservation Laws The first astrophysics we ll consider will be gravity, which we ll address in the next class. First, though, we need to set the stage by talking about some of the basic

### Lecture L3 - Vectors, Matrices and Coordinate Transformations

S. Widnall 16.07 Dynamics Fall 2009 Lecture notes based on J. Peraire Version 2.0 Lecture L3 - Vectors, Matrices and Coordinate Transformations By using vectors and defining appropriate operations between

### Solutions to Problems in Goldstein, Classical Mechanics, Second Edition. Chapter 7

Solutions to Problems in Goldstein, Classical Mechanics, Second Edition Homer Reid April 21, 2002 Chapter 7 Problem 7.2 Obtain the Lorentz transformation in which the velocity is at an infinitesimal angle

### SCATTERING CROSS SECTIONS AND LORENTZ VIOLATION DON COLLADAY

SCATTERING CROSS SECTIONS AND LORENTZ VIOLATION DON COLLADAY New College of Florida, 5700 Tamiami Trail, Sarasota, FL 34243, USA E-mail: colladay@sar.usf.edu To date, a significant effort has been made

### 1 Lecture 3: Operators in Quantum Mechanics

1 Lecture 3: Operators in Quantum Mechanics 1.1 Basic notions of operator algebra. In the previous lectures we have met operators: ˆx and ˆp = i h they are called fundamental operators. Many operators

### 4. The Infinite Square Well

4. The Infinite Square Well Copyright c 215 216, Daniel V. Schroeder In the previous lesson I emphasized the free particle, for which V (x) =, because its energy eigenfunctions are so simple: they re the

### Basic Quantum Mechanics Prof. Ajoy Ghatak Department of Physics. Indian Institute of Technology, Delhi

Basic Quantum Mechanics Prof. Ajoy Ghatak Department of Physics. Indian Institute of Technology, Delhi Module No. # 02 Simple Solutions of the 1 Dimensional Schrodinger Equation Lecture No. # 7. The Free

### Introduces the bra and ket notation and gives some examples of its use.

Chapter 7 ket and bra notation Introduces the bra and ket notation and gives some examples of its use. When you change the description of the world from the inutitive and everyday classical mechanics to

### Introduction to Matrix Algebra

Psychology 7291: Multivariate Statistics (Carey) 8/27/98 Matrix Algebra - 1 Introduction to Matrix Algebra Definitions: A matrix is a collection of numbers ordered by rows and columns. It is customary

### Supplemental Worksheet Problems To Accompany: The Pre-Algebra Tutor: Volume 1 Section 5 Subtracting Integers

Supplemental Worksheet Problems To Accompany: The Pre-Algebra Tutor: Volume 1 Please watch Section 5 of this DVD before working these problems. The DVD is located at: http://www.mathtutordvd.com/products/item66.cfm

### How is a vector rotated?

How is a vector rotated? V. Balakrishnan Department of Physics, Indian Institute of Technology, Madras 600 036 Appeared in Resonance, Vol. 4, No. 10, pp. 61-68 (1999) Introduction In an earlier series

### 1 Eigenvalues and Eigenvectors

Math 20 Chapter 5 Eigenvalues and Eigenvectors Eigenvalues and Eigenvectors. Definition: A scalar λ is called an eigenvalue of the n n matrix A is there is a nontrivial solution x of Ax = λx. Such an x

### Unified Lecture # 4 Vectors

Fall 2005 Unified Lecture # 4 Vectors These notes were written by J. Peraire as a review of vectors for Dynamics 16.07. They have been adapted for Unified Engineering by R. Radovitzky. References [1] Feynmann,

### Quantum Mechanics: Postulates

Quantum Mechanics: Postulates 5th April 2010 I. Physical meaning of the Wavefunction Postulate 1: The wavefunction attempts to describe a quantum mechanical entity (photon, electron, x-ray, etc.) through

### Linear Dependence Tests

Linear Dependence Tests The book omits a few key tests for checking the linear dependence of vectors. These short notes discuss these tests, as well as the reasoning behind them. Our first test checks

### Lecture Notes for Ph219/CS219: Quantum Information and Computation Chapter 2. John Preskill California Institute of Technology

Lecture Notes for Ph19/CS19: Quantum Information and Computation Chapter John Preskill California Institute of Technology Updated July 015 Contents Foundations I: States and Ensembles 3.1 Axioms of quantum

### Introduction to Matrix Algebra I

Appendix A Introduction to Matrix Algebra I Today we will begin the course with a discussion of matrix algebra. Why are we studying this? We will use matrix algebra to derive the linear regression model

### PHY4604 Introduction to Quantum Mechanics Fall 2004 Practice Test 3 November 22, 2004

PHY464 Introduction to Quantum Mechanics Fall 4 Practice Test 3 November, 4 These problems are similar but not identical to the actual test. One or two parts will actually show up.. Short answer. (a) Recall

### - develop a theory that describes the wave properties of particles correctly

Quantum Mechanics Bohr's model: BUT: In 1925-26: by 1930s: - one of the first ones to use idea of matter waves to solve a problem - gives good explanation of spectrum of single electron atoms, like hydrogen

### 3. A LITTLE ABOUT GROUP THEORY

3. A LITTLE ABOUT GROUP THEORY 3.1 Preliminaries It is an apparent fact that nature exhibits many symmetries, both exact and approximate. A symmetry is an invariance property of a system under a set of

### Computer Graphics Prof. Sukhendu Das Dept. of Computer Science and Engineering Indian Institute of Technology, Madras Lecture 7 Transformations in 2-D

Computer Graphics Prof. Sukhendu Das Dept. of Computer Science and Engineering Indian Institute of Technology, Madras Lecture 7 Transformations in 2-D Welcome everybody. We continue the discussion on 2D

### Matrix Algebra and Applications

Matrix Algebra and Applications Dudley Cooke Trinity College Dublin Dudley Cooke (Trinity College Dublin) Matrix Algebra and Applications 1 / 49 EC2040 Topic 2 - Matrices and Matrix Algebra Reading 1 Chapters

### 5.61 Physical Chemistry 25 Helium Atom page 1 HELIUM ATOM

5.6 Physical Chemistry 5 Helium Atom page HELIUM ATOM Now that we have treated the Hydrogen like atoms in some detail, we now proceed to discuss the next simplest system: the Helium atom. In this situation,

### Quantum Chemistry Exam 2 Solutions (Take-home portion)

Chemistry 46 Spring 5 Name KEY Quantum Chemistry Exam Solutions Take-home portion 5. 5 points In this problem, the nonlinear variation method will be used to determine approximations to the ground state

### Mechanics 1: Conservation of Energy and Momentum

Mechanics : Conservation of Energy and Momentum If a certain quantity associated with a system does not change in time. We say that it is conserved, and the system possesses a conservation law. Conservation

### PHY4604 Introduction to Quantum Mechanics Fall 2004 Practice Exam Solutions Dec. 13, 2004

PHY4604 Introduction to Quantum Mechanics Fall 2004 Practice Exam Solutions Dec. 1, 2004 No materials allowed. If you can t remember a formula, ask and I might help. If you can t do one part of a problem,

### CHAPTER 5 THE HARMONIC OSCILLATOR

CHAPTER 5 THE HARMONIC OSCILLATOR The harmonic oscillator is a model which has several important applications in both classical and quantum mechanics. It serves as a prototype in the mathematical treatment

### Generally Covariant Quantum Mechanics

Chapter 15 Generally Covariant Quantum Mechanics by Myron W. Evans, Alpha Foundation s Institutute for Advance Study (AIAS). (emyrone@oal.com, www.aias.us, www.atomicprecision.com) Dedicated to the Late

### MATRIX ALGEBRA AND SYSTEMS OF EQUATIONS

MATRIX ALGEBRA AND SYSTEMS OF EQUATIONS Systems of Equations and Matrices Representation of a linear system The general system of m equations in n unknowns can be written a x + a 2 x 2 + + a n x n b a

### Appendix E - Elements of Quantum Mechanics

1 Appendix E - Elements of Quantum Mechanics Quantum mechanics provides a correct description of phenomena on the atomic or sub- atomic scale, where the ideas of classical mechanics are not generally applicable.

### Linear Algebra Notes

Linear Algebra Notes Chapter 19 KERNEL AND IMAGE OF A MATRIX Take an n m matrix a 11 a 12 a 1m a 21 a 22 a 2m a n1 a n2 a nm and think of it as a function A : R m R n The kernel of A is defined as Note

### Inverses and powers: Rules of Matrix Arithmetic

Contents 1 Inverses and powers: Rules of Matrix Arithmetic 1.1 What about division of matrices? 1.2 Properties of the Inverse of a Matrix 1.2.1 Theorem (Uniqueness of Inverse) 1.2.2 Inverse Test 1.2.3

### Additional Topics in Linear Algebra Supplementary Material for Math 540. Joseph H. Silverman

Additional Topics in Linear Algebra Supplementary Material for Math 540 Joseph H Silverman E-mail address: jhs@mathbrownedu Mathematics Department, Box 1917 Brown University, Providence, RI 02912 USA Contents

### Gauge theories and the standard model of elementary particle physics

Gauge theories and the standard model of elementary particle physics Mark Hamilton 21st July 2014 1 / 35 Table of contents 1 The standard model 2 3 2 / 35 The standard model The standard model is the most

### 1 Anomalies and the Standard Model

1 Anomalies and the Standard Model The Glashow-Weinberg-Salam model of the electroweak interactions has been very successful in explaining a wide range of experimental observations. The only major prediction

### Regression Analysis Prof. Soumen Maity Department of Mathematics Indian Institute of Technology, Kharagpur. Lecture - 2 Simple Linear Regression

Regression Analysis Prof. Soumen Maity Department of Mathematics Indian Institute of Technology, Kharagpur Lecture - 2 Simple Linear Regression Hi, this is my second lecture in module one and on simple

### Name: Section Registered In:

Name: Section Registered In: Math 125 Exam 3 Version 1 April 24, 2006 60 total points possible 1. (5pts) Use Cramer s Rule to solve 3x + 4y = 30 x 2y = 8. Be sure to show enough detail that shows you are

### MATH10212 Linear Algebra. Systems of Linear Equations. Definition. An n-dimensional vector is a row or a column of n numbers (or letters): a 1.

MATH10212 Linear Algebra Textbook: D. Poole, Linear Algebra: A Modern Introduction. Thompson, 2006. ISBN 0-534-40596-7. Systems of Linear Equations Definition. An n-dimensional vector is a row or a column

### 2 Session Two - Complex Numbers and Vectors

PH2011 Physics 2A Maths Revision - Session 2: Complex Numbers and Vectors 1 2 Session Two - Complex Numbers and Vectors 2.1 What is a Complex Number? The material on complex numbers should be familiar

### CHAPTER 16: Quantum Mechanics and the Hydrogen Atom

CHAPTER 16: Quantum Mechanics and the Hydrogen Atom Waves and Light Paradoxes in Classical Physics Planck, Einstein, and Bohr Waves, Particles, and the Schrödinger equation The Hydrogen Atom Questions

### Quantum Field Theory and Representation Theory

Quantum Field Theory and Representation Theory Peter Woit woit@math.columbia.edu Department of Mathematics Columbia University Quantum Field Theory and Representation Theory p.1 Outline of the talk Quantum

### Solving a System of Equations

11 Solving a System of Equations 11-1 Introduction The previous chapter has shown how to solve an algebraic equation with one variable. However, sometimes there is more than one unknown that must be determined

### Meson cloud effects in the electromagnetic hadron structure

Meson cloud effects in the electromagnetic hadron structure Daniel Kupelwieser Thesis supervisor: Wolfgang Schweiger Collaborators: Elmar Biernat, Regina Kleinhappel Universität Graz Graz Jena monitoring

### = [a ij ] 2 3. Square matrix A square matrix is one that has equal number of rows and columns, that is n = m. Some examples of square matrices are

This document deals with the fundamentals of matrix algebra and is adapted from B.C. Kuo, Linear Networks and Systems, McGraw Hill, 1967. It is presented here for educational purposes. 1 Introduction In

### Theory of electrons and positrons

P AUL A. M. DIRAC Theory of electrons and positrons Nobel Lecture, December 12, 1933 Matter has been found by experimental physicists to be made up of small particles of various kinds, the particles of

### Further Maths Matrix Summary

Further Maths Matrix Summary A matrix is a rectangular array of numbers arranged in rows and columns. The numbers in a matrix are called the elements of the matrix. The order of a matrix is the number

### Quantum Mechanics and Representation Theory

Quantum Mechanics and Representation Theory Peter Woit Columbia University Texas Tech, November 21 2013 Peter Woit (Columbia University) Quantum Mechanics and Representation Theory November 2013 1 / 30

### Topic 1: Matrices and Systems of Linear Equations.

Topic 1: Matrices and Systems of Linear Equations Let us start with a review of some linear algebra concepts we have already learned, such as matrices, determinants, etc Also, we shall review the method

### The Phase Plane. Phase portraits; type and stability classifications of equilibrium solutions of systems of differential equations

The Phase Plane Phase portraits; type and stability classifications of equilibrium solutions of systems of differential equations Phase Portraits of Linear Systems Consider a systems of linear differential

### Lecture 22 Relevant sections in text: 3.1, 3.2. Rotations in quantum mechanics

Lecture Relevant sections in text: 3.1, 3. Rotations in quantum mechanics Now we will discuss what the preceding considerations have to do with quantum mechanics. In quantum mechanics transformations in

### Solutions to Math 51 First Exam January 29, 2015

Solutions to Math 5 First Exam January 29, 25. ( points) (a) Complete the following sentence: A set of vectors {v,..., v k } is defined to be linearly dependent if (2 points) there exist c,... c k R, not

### - the total energy of the system is found by summing up (integrating) over all particles n(ε) at different energies ε

Average Particle Energy in an Ideal Gas - the total energy of the system is found by summing up (integrating) over all particles n(ε) at different energies ε - with the integral - we find - note: - the

### The Standard Model of Particle Physics

Andrea Romanino Associate Professor, SISSA. The scientific interests include Standard Model and beyond, including supersymmetry, extra dimensions and grand unification; flavour and neutrino physics. Abstract:

### Contents. Goldstone Bosons in 3He-A Soft Modes Dynamics and Lie Algebra of Group G:

... Vlll Contents 3. Textures and Supercurrents in Superfluid Phases of 3He 3.1. Textures, Gradient Energy and Rigidity 3.2. Why Superfuids are Superfluid 3.3. Superfluidity and Response to a Transverse

### Chapter 9 Unitary Groups and SU(N)

Chapter 9 Unitary Groups and SU(N) The irreducible representations of SO(3) are appropriate for describing the degeneracies of states of quantum mechanical systems which have rotational symmetry in three

### Chapter 8. Matrices II: inverses. 8.1 What is an inverse?

Chapter 8 Matrices II: inverses We have learnt how to add subtract and multiply matrices but we have not defined division. The reason is that in general it cannot always be defined. In this chapter, we

### Topologically Massive Gravity with a Cosmological Constant

Topologically Massive Gravity with a Cosmological Constant Derek K. Wise Joint work with S. Carlip, S. Deser, A. Waldron Details and references at arxiv:0803.3998 [hep-th] (or for the short story, 0807.0486,

### The Equation of State

The Equation of State The equation of state is the function that relates the pressure to the density, molecular weight, and temperature at any place in the star. Since it is a solely an internal property

### Time dependence in quantum mechanics Notes on Quantum Mechanics

Time dependence in quantum mechanics Notes on Quantum Mechanics http://quantum.bu.edu/notes/quantummechanics/timedependence.pdf Last updated Thursday, November 20, 2003 13:22:37-05:00 Copyright 2003 Dan