Quantum-ElectroDynamics (QED) is the quantum field theory believed to describe the electromagnetic interaction (and with some extension the weak nuclear force).

learn more… | top users | synonyms (1)

9
votes
2answers
402 views

Peskin's book page 334 proof of $Z_1=Z_2$ to all orders in QED perturbation theory

Peskin in his QFT page 334 argued that $Z_1=Z_2$ to all orders in QED perturbation theory, but I couldn't understand his argument: ... With a generalization of the argument given there (section ...
0
votes
1answer
21 views

Magnetic field of a current carrying wire reduce/increase exterior magnetic field?

If we place a wire within a uniform exterior magnetic field ($B_x$) that's perpendicular to it's length, and allowed current to flow withing the that conductive medium, there is another magnetic field ...
0
votes
0answers
45 views

Atom - light field coupling and emission process

Suppose a "2-state atom" and a light field are quantized with the following Hamiltonians, respectively: $$\hat{H}_A=\hbar\omega_{21}\hat{\sigma}^{\dagger}\hat{\sigma}$$ and ...
1
vote
0answers
30 views

Lamb shift and logarithmic corrections

Radiative corrections (Lamb shift) to the energy level (1S state) of a hydrogen atom can be written as a power series in $Z\alpha$ and $\ln(Z\alpha)$: $$\Delta E = \frac{\alpha}{\pi}(Z\alpha)^4 ...
2
votes
1answer
108 views

Quantized light-atom Hamiltonian

Suppose a "2-state atom" and a light field are quantized with the following Hamiltonians, respectively: $$\hat{H}_A=\hbar\omega_{21}\hat{\sigma}^{\dagger}\hat{\sigma}$$ and ...
6
votes
1answer
435 views

What exactly is the connection between gauge transformations and symmetry groups?

For a given gauge transformation, say, the electromagnetic field, where observable quantities aren't affected by transformations of the form $$\mathbf{A}' = \mathbf{A} + \nabla \chi,$$ $$\phi' = \phi ...
1
vote
0answers
24 views

Implications for measurement of an initially localized free particle's wavefunction spreading out to infinity?

So, I have been attempting to wrap my head around what happens to a free particle that is initially localized to one spot. It seems that due to their different frequencies, the particle's wavefunction ...
2
votes
1answer
41 views

Absorption of photon as particle by an electron

As the photon gets absorbed by the electron and goes to higher energy state, does the photon remains in the electron itself in some form (radiation energy), thereby increasing the mass of electron?
4
votes
3answers
79 views

Do we know why the field produced by charge extends to infinity?

Do we have any model to show why charge field or magnetic field extends till infinity. Edit: I agree that according to coulombs law $1/r^2$ cannot be 0 but do we know why this happens.I think I am ...
0
votes
0answers
13 views

NLO compton scattering

I have a question about the NLO processes, that contribute to ${\mid M \mid}^2$ with ${\alpha}^3$ in compton scattering. I can see, that an extra radiative $\gamma$ gives terms $\propto {\alpha}^3$. ...
1
vote
1answer
49 views

Is Huygens's Wave Theory still correct?

We have to study on details about Huygens's Wave Theory though we have Electromagnetic theory, quantum theory today. Is it still correct or not?
1
vote
0answers
15 views

How to calculate the magnetic field due to orbital angular momentum in the fine structure

How to calculate effective magnetic field due to the angular momentum L in an atom like Na(23)? I found an answer that we could imagine the case that the atom was orbiting the electron now and ...
10
votes
1answer
186 views

Why very strong fields are required for a photon to split?

Photon splitting does not occur in free space as energy and momentum cannot be conserved in any Lorentz frame. But it does occur in the presence of a strong field. Consider the example of a Magnetar. ...
1
vote
0answers
53 views

Electron matrix element in a most simple QFT problem, the e+ e- annihilation

In the beginning of my new QFT book there is this short chapter called Invitation: Pair Production in $e^{+}$ $e^{-}$ Annihilation. An electron and a positron collide and a couple muon & antimuon ...
1
vote
0answers
30 views

Does energy transmission depend on the speed of incoming particle?

Since a few past days , I am struggling with finding an in depth atomic model of force exchange between colliding paricles (originally newtons third law) , because at this point of time i am unable to ...
1
vote
1answer
114 views

Explanation for Refraction of light (change of angle) and Reflection

Refraction: I want a qualitative Quantum Mechanical explanation of why do we see light rays -in the classical picture- bend when light goes from one medium to another. I read that it is due to ...
1
vote
0answers
42 views

What would happen if a monochromatic light falls on an electron?

An electron is not strictly free, but in terms of QFT, we consider scattering events in an asymptotic framework where free particles would arise at $t \rightarrow \pm \infty$. So, I would like to know ...
0
votes
0answers
36 views

Help in writing down Feynman rule? [duplicate]

I have a term in my Lagrangian that looks like: $A^\mu B^{*\nu} \partial_\mu B_\nu - A^\nu B^{* \mu} \partial_\mu B_\nu$ where A is the photon field, and B is a charged, massive spin-1 boson. I am ...
2
votes
0answers
93 views

What prevents this third-order QED scattering from having a non-zero amplitude?

I have learned that in the Dyson-Wick expansion of the QED scattering operator $$ S=e^{-i\int_{t_i}^{t_f}H\mathrm{d}t} $$ with the QED interaction Lagrangian $$ H=e\bar\psi\gamma^\mu A_\mu\psi $$ ...
1
vote
0answers
61 views

Does this vertex equal 0?

If I have an interaction term in my Lagrangian that looks like: $\mathcal{L}_{int} = (\partial_\mu B_\nu)(A^\mu B^\nu - A^\nu B^\mu)$ where B is a massive spin-1 field. Am I correct in thinking that ...
0
votes
1answer
36 views

Good book on quantum photonics and applications

I am just looking for an easy to read introduction to quantum photonics and possible applications. Terms like "Fock state" and "Photon (anti)bunching" should be understood after reading. Perhaps also ...
3
votes
0answers
38 views

Second order quantum coherence function

I have one question from the course of quantum optics. In general the second order quantum coherence in time is defined as, $$g^{(2)}(\tau)=\frac{\left\langle ...
6
votes
6answers
2k views

How is the double slit experiment modeled in contemporary physical theories?

Suppose I have the following double split experiment set up: a monochromatic electron source of low intensity, which we can model as emitting a single electron at a time with energy $T$. a ...
2
votes
0answers
61 views

Classical electrodynamics as an $\mathrm{U}(1)$ gauge theory

Preface: I haven't studied QED or any other QFT formally, only by occasionally flipping through books, and having a working knowledge of the mathematics of gauge theories (principal bundles, etc.). ...
2
votes
1answer
72 views

What is spin in QFT, non-relativistic QM, and classical physics? When can we ignore spin? [closed]

In section 4.1.1 of quantum field theory book by M. Schwartz, the author wants to calculate electron scattering by photons and writes the following interaction: $$ V= \frac{1}{2}e\int dx ...
2
votes
0answers
161 views

What is the effective (quantum) lagrangian of a fermion field for fixed electromagnetic field?

... or, put it another way, what are the loop corrections to the dirac equation in the presence of a fixed (external) electromagnetic field?. Background Let $\mathcal ...
3
votes
2answers
490 views

Is there a way to calculate the photoelectric effect in QED via a Feynman diagram?

The photoelectric effect is the historic origin of the quantum particle description of light. From it we learn that when light is shone onto a metal single photons interact with single electrons in ...
9
votes
2answers
2k views

What's the relation between virtual photons and electromagnetic potentials?

Given that: 1) virtual photons mediate the electric and magnetic force fields 2) the magnetic field is the curl of the magnetic vector potential 3) the electric field is the negative gradient of ...
1
vote
2answers
139 views

How does exciting an electron's surrounding electromagnetic field cause 'electron excitation'?

In more meaningful words than the ones above, how does adding energy to the EM field cause the electron to to change orbitals or oscillate in a different pattern.
1
vote
1answer
105 views

Analyzing electron-positron scattering cross section in detail

It can be found in any quantum electrodynamics book that the cross section for electron-positron scattering in the high energy limit is \begin{equation} \dfrac{\mathrm{d} \sigma}{\sin \theta \, ...
1
vote
1answer
55 views

By what mechanism is a photon emitted or absorbed in atomic electron state transitions?

I understand atomic emission and absorption spectra well - photons of a specific energy can be emitted or absorbed by atoms, if that energy corresponds perfectly to the energy difference between two ...
3
votes
3answers
126 views

Which elementary particles are behind magnetic field, similar as photons behind radio waves?

I see, there are photons behind radio waves. As Wave–particle duality said: the radio waves are waves and at the same time are fluxes of particles called Photons. I'm wondering, what is behind ...
3
votes
1answer
99 views

Why do we require local gauge invariance

My thought on this are somewhat scattered so I apologise in advance. Maxwell's equations are gauge invariant. The physical Electric and Magnetic fields don't depend on whether we use $A_\mu$ or ...
9
votes
5answers
6k views

Spontaneous pair production?

So I've been looking into particle-antiparticle pair production from a gamma ray and don't understand one thing. Let's say I have a 1,1 MeV photon and it hits a nucleus - electron-positron pair with ...
3
votes
1answer
76 views

Doubt in Dyson's argument about the divergent nature of the perturbative expansion in QED

I am trying to understand Dyson's argument about the divergent nature of the perturbative expansion in QED. Quoting his own words [...] let $$F(e^2)=a_0+a_1e^2+a_2e^4+\ldots$$ be a physical ...
1
vote
1answer
262 views

Free electromagnetic field in Lorenz gauge

To get rid of the extra term in the QED Lagrangian we need to redefine the electromagnetic four-vector: $A^{\mu} \rightarrow A^{\mu} - \frac{1}{c} \partial_{\mu} a(x)$ where $a(x)$ is the function ...
2
votes
3answers
8k views

Can a light be bent by a magnetic field?

I'm struck with two competing ideas on the question in the title. Listing #1: http://van.physics.illinois.edu/qa/listing.php?id=2009 How far can a magnetic field bend light? A: Unfortunately, the ...
1
vote
1answer
32 views

QCD-Process with superposition-particle

I am a total beginner with non-abelian gauges. To write down a process from a neutral pion ($\pi^0 = \frac{1}{\sqrt{2}}(u\overline{u}-d\overline{d})$) I expect to have to write it as this ...
2
votes
0answers
46 views

Why not 2, 3, 4, or more photons can be absorbed by single electron? [duplicate]

During Photoelectric effect and other such phenomenon, when light is made to fall on metal surface, single photon is absorbed by the single electron present in metal atom. Why not 2, 3, 4, or more ...
1
vote
0answers
15 views

Threshold voltage for townsend avalanche effect [closed]

I have an assignment to estimate the minimal voltage required for an avalanche effect to occur. All data I am given is electron energy (10eV) and pressure of the ...
0
votes
1answer
43 views

Electro-mangetic duality, Quantum electro dynamics and N=4 SYM

This question is extension of Electro magnetic duality, Strong weak duality and N=4 super Yangmils which i asked before. Here what i want to know is compare of QED and N=4 SYM in terms of ...
3
votes
1answer
40 views

Why Conserved Current Should Not Need Renormalization?

May be this is trivial but I need to understand why the renormalization of conserved current is not necessary ? As for example, in this paper, they demand (2$^{nd}$ paragraph of the 2$^{nd}$ column in ...
3
votes
1answer
438 views

What does the magnetic field of the (quantum-mechanical) electron look like?

While a treatment of electron spin can be found in any introductory textbook, I've noticed that the electron's magnetic field seems to be treated classically. Presumably this is because a quantum ...
1
vote
1answer
54 views

Electro magnetic duality, Strong weak duality and N=4 super Yangmils

How we can interpret this self-dual, or duality in terms of generalized version of electro magneitc duality, or Strong weak duality. Let me address some basic information. First, electro magnetic ...
0
votes
3answers
105 views

About quantization of EM energy for amplitude-modulated wave

Consider an electromagnetic monochromatic plane wave at frequency $f$ and E-field amplitude $E_0$ in vacuum. From the quantum electrodynamics point of view, we could say that the energy that EM wave ...
0
votes
1answer
69 views

Looking for a reference for $\gamma_a e^{a}_{\mu} D^\mu \gamma_b e^{b}_{\nu} D^\nu =D^\mu D_\mu - \tfrac{1}{4}R$

I am having trouble finding references for the following identities: Dirac Operator: $$ \gamma_a e^{a}_{\mu} D^\mu \gamma_b e^{b}_{\nu} D^\nu =D^\mu D_\mu - \tfrac{1}{4}R \tag{1} $$ QED Operator: $$ ...
0
votes
0answers
28 views

Feynman diagrams with ghosts and symmetry breaking

Let us think of an abelian gauge theory, precisely a scalar QED with 3 complex components of the scalar field and a 4-degree auto-interaction mixing components. Let us consider a spontaneously ...
3
votes
1answer
100 views

Are atoms unstable in 4+1 dimensions when quantum mechanics is taken into account?

I understand that in 3+1 dimensions according to classical physics atoms should be unstable however atoms are stable in 3+1 dimensions because the behavior of atoms is governed by quantum physics ...
3
votes
2answers
247 views

Negative mass dirac equation -> Propagator?

There are two types of dirac equations: $(p_\mu\gamma^\mu - m)\Psi(x) = 0$ and $(p_\mu\gamma^\mu + m)\Psi(x) = 0$. Here $p$ are the momentum operators. The fermion propagator is defined in the ...
-1
votes
1answer
55 views

Why the QED coupling constant is a continuous function? [closed]

In page 316 of 'Student friendly quantum field theory', when discussing Figure 12-4, it says that the QED coupling constant is a continuous function of $\ln(p)$. But I think it's disconnected at ...