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)

3
votes
2answers
837 views

Where does the mass term come from in the Proca Lagrangian?

There are many good books describing how to construct the Lagrangian for an electromagnetic field in a medium. $$ \mathcal{L}~=~-\frac{1}{16\pi}F^{\mu\nu}F_{\mu\nu}-\frac{1}{c}j^{\nu}A_{\nu} $$ ...
3
votes
2answers
305 views

Energy spectrum of a Dirac electron

How do you explain easily "The spectrum of an electron in a repulsive potential " and hence "bound state of charge conjugation" in Dirac hole theory ?
3
votes
3answers
130 views

QED as a Wightman theory of observable fields? With a collision theory?

[Note: I'm using QED as a simple example, despite having heard that it is unlikely to exist. I'm happy to confine the question to perturbation theory.] The quantized Aᵘ and ψ fields are non-unique ...
3
votes
1answer
425 views

What is Electromagnetic Induced Transparency?

Please can anyone explain the concepts of electromagnetic induced transparency? I am having problem with the technicality of the explanation on wikipedia. Please I am an engineer with a physics ...
3
votes
1answer
41 views

Why is the frequency bandwidth of the environment important for Markovianity?

In the derivation of Spontaneous Emission in two level systems in Quantum Optics (be it Wigner Weisskopf or a different approach, such as density operators to find the master equation), one makes ...
3
votes
1answer
71 views

Time reversal invariance and boundary conditions in electrodynamics

This is really several related questions... The equations of classical electrodynamics are time-reversal invariant. However, when we solve the equations for a particular system of charges it is ...
3
votes
1answer
177 views

Did the Goudsmit-Uhlenbeck analysis of spin consider relativity?

It's frequently mentioned in introductory quantum mechanics texts that Goudsmit and Uhlenbeck conjectured that the magnetic moment of an electron was due to angular momentum arising from the electron ...
3
votes
1answer
193 views

The state of Indefinite metric in Quantum Electrodynamics

I faced difficulties to grasp why indefinite metric is introduced from no where in QED, after searching internet I found that this is a problem in QED, because one needs it to preserve theory's ...
3
votes
1answer
149 views

Is there any analogy between electron positron annihilation and brane anti-brane annihilation?

I would like to know if there is any similarity between electron positron annihilation and brane anti-brane annihilation? Is it there then can we use electron positron annihilation knowledge to study ...
3
votes
1answer
314 views

Effects of parallel superconducting plates

Assuming the existence of virtual particle field ( zero point energy field) Casimir force is produced by 2 parallel conducting plates excluding some of the frequencies between the plates, if these 2 ...
3
votes
0answers
65 views

What is the phase space for outgoing photons?

For a scattering process for which $n$ fermions are scattered, (by some conventions) the cross section acquires a phase space factor of: $$d\sigma \sim \prod_{i=1}^n\frac{d^3p_i}{(2\pi)^3 2E_i}$$ ...
3
votes
0answers
121 views

Double Slit Experiment with Two Independent Sources

Imagine a variation on the double slit experiment. I'll describe it in 2D using the $x-y$ plane. The $x$-axis is impenetrable other than the two slits, which are positioned at $(-1,0)$ and $(+1,0)$. ...
3
votes
0answers
103 views

Vector potential and gauge in electromagnetism

In a paper by Zimmerman [JOURNAL OF APPLIED PHYSICS 114, 044907 (2013)], it is stated that the Lorenz gauge in electromagnetism is the only gauge with real physical meaning. How do I reconcile this ...
3
votes
0answers
274 views

How to understand the QED, QCD and standard model Lagrangians? [closed]

How do you read the QED, QCD and standard model Lagrangians? What do all the symbols and tensors represent? And, how can you derive them by yourselves?
3
votes
0answers
717 views

Proof of Furry's theorem

i was wondering if anyone could give an explicit calculation or show a link that shows the proof to Furry's theorem. showing how the vacuum expectation value of any odd number of electromagnetic ...
3
votes
1answer
456 views

Evaluation of QED amplitude with 1 external photon

I'm trying to compute the exact QED amplitude with one external photon. Suppose that the photon has 4-momentum $q$ and polarization $\varepsilon^\mu$. Peskin and Schroeder (p318) claim that ignoring ...
3
votes
0answers
105 views

experiment proposal to validate microcausality

I've been wondering about microcausality for some time now (a recent question of mine regarding the topic) and i'm wondering if its possible to devise an experiment to detect potential violations I ...
3
votes
0answers
172 views

Transition of electric charge to “magnetic charge” when $\alpha$ gets >> 1 in QED?

I`ve just learned that electrically charged particles and magnetically charged monopoles in QED are S-dual to each other such that it depends on the value of the fine structure constant which of the ...
3
votes
3answers
121 views

Why most of physics is somehow related to light? [closed]

It seems that for the past 200 years, every physicist is concerned about light. For example : Newton's particle model, Young experiment, Photo-Electrict effect and Einstein's formula, Special ...
3
votes
1answer
239 views

'Validity' of QED/QCD/Electroweak interaction

I am currently attending a course on Quantum Field Theory and I got into thinking how valid these theories are. As the theory attempts to describe reality only far above the Planck (length) scale, ...
2
votes
1answer
322 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 ...
2
votes
1answer
297 views

Experimental proof of gravitational redshift of light

Has the gravitational red shift been proven for electromagnetic waves only or also for a single photon?
2
votes
2answers
140 views

Are electron fields and photon fields part of the same field in QED?

I know in classical field theory we have the electromagnetic field. And Maxwell's equations show how electromagnetic radiation can propagate through empty space. I also have been reading about QED ...
2
votes
1answer
206 views

Mølller scattering

I came across Mølller scattering today (which is just a fancy name for electron-electron scattering. I'm confused as to why there are two tree level Feynman diagrams for this process: Check out the ...
2
votes
2answers
521 views

proof of radius of convergence of perturbation series in quantum electrodynamics zero

Can anyone show detailed proof of why radius of convergence of perturbation series in quantum electrodynamics is zero? And how is perturbation series constructed? So, as this argument requires ...
2
votes
2answers
211 views

Deriving the Coulomb force equation from the idea of photon exchange?

Since Newton's law of gravitation can be gotten out of Einstein's field equatons as an approximation, I was wondering whether the same applies for the electromagnetic force being the exchange of ...
2
votes
2answers
682 views

Mass dimension of coupling constants in various dimensions

Just a quick question: Suppose I want to consider QED or YM in 4 dimensions we always say that the coupling constants are dimensionless and that the field then has a specific mass dimension. What ...
2
votes
2answers
532 views

Is wave–particle duality considered a valid interpretation of the behavior of photons?

There are a number of questions on this site that explain the many wave-like behaviors of photons by making reference to wave-particle duality. However, I have just finished reading Feynman's book ...
2
votes
1answer
730 views

Hyperfine structure vs Lamb shift in the hydrogen atom

The hyperfine structure of the energy levels of the hydrogen atom refers to the shifts in the evergy levels due to the magnetic moments of the nucleus and of the electron. This is an effect of ...
2
votes
1answer
59 views

What is $Q_p/Q_e$ experimentally? [duplicate]

What is the experimental value of the ratio between the proton and the electron charge? Or more generally, is there a table that lists the ratio of the different nuclei charges to that of the ...
2
votes
1answer
71 views

Is the QED description of an electron/photon complete?

Is it possible that a future theory would add more information and understanding about electrons, photons etc., or is QED the best we can do?
2
votes
1answer
213 views

Christoffel symbols and Dirac matrices mathematical similarities?

Maybe mine is a silly question, but are there mathematical similarities or common roots between the Christoffel symbols: $ \nabla - \partial = \Gamma $ and the Dirac matrices $ ( \gamma^\mu ...
2
votes
1answer
181 views

Understanding the argument that local U(1) leads to coupling of EM and matter

I'm trying to better understand the argument that U(1) local gauge invariance implies a coupling of EM and Dirac fields. I understand the math, but I'm not sure about the chain of logic. You start ...
2
votes
3answers
528 views

What starts the movement of a photon

Although a photon has no (rest) mass, it does have a measurable speed. Its movement can be altered by gravity. A photon "travels". If I turn on a flashlight, seen by someone at a distance, the photons ...
2
votes
1answer
183 views

Is there a simple explanation for Schwinger's relation $g=2+\frac{\alpha}{\pi}+{\cal O}(\alpha^2)$ for the $g$-factor of the electron?

Schwinger has on his grave (it seems) the relation between the g-factor of the electron and the fine structure constant: $$g~=~2+\frac{\alpha}{\pi}+{\cal O}(\alpha^2)$$ Did Schwinger or somebody ...
2
votes
1answer
46 views

Basic QED - How are conserved charges expressions throught ladder operators derived?

I can't find this in similar questions, and I must be missing something very basilar since I can't find this in any textbook or online note: they just skip the passage. So, from my course's notes, we ...
2
votes
1answer
66 views

Fermion propagator decomposition

I've seen the following decomposition for the fermion propagator for a fermion with momenta $p-k$, and where both $p-k$ and $p$ have a mass of $m$: $$\frac{(\not p-\not k)+m}{(p-k)^2-m^2}\gamma_\mu= ...
2
votes
1answer
62 views

Large wavelength limit of gluons

Does there exist a classical limit of QCD? I mean in the sense of wave particle duality of eg photons. Is there any similar thing for gluons?
2
votes
1answer
275 views

Value of weak force coupling constant

I'm trying to get my head around the weak force coupling constant $\alpha_w$ but getting confused by different resources. Hyperphysics suggests it is tiny compared with the strong force coupling, ...
2
votes
1answer
83 views

Can a single photon induce current in a very small coil?

As I know from Lenz's law, I can induce current in a coil just by changing the magnetic field flux inside the coil. As I know from physics course, photons are electromagnetic waves (so they are the ...
2
votes
2answers
47 views

What is light localisation?

Reading about plasmonic nanoparticles I faced the term "localised light". How can one localise light? What are applications of it?
2
votes
1answer
116 views

What is Photoproduction

I wonder what photoproduction means in the context of pion decay and vector meson dominance? What is the reaction formula, Feynman diagram for such a photoproduction thing? Is it simply a reaction ...
2
votes
1answer
201 views

Vacuum polarization in QCD and gluon bubbles

In analogy to QED, the following Feynman diagram is a diagram contributing to the vacuum polarization effect, leading to anti-screening, asymptotic freedom and running of the strong coupling constant. ...
2
votes
1answer
1k views

Photons, where do they come from? [closed]

Photons, where do they come from? What exactly is a photon? I've certainly heard how they get produced, but it doesn't seem to make sense that some sort of particle should need to be produced just ...
2
votes
1answer
318 views

Which is this formula Feynman talks about in the QED book?

I am reading the fantastic QED Feynman book. He talks in chapter 3 about a formula he considers too complicated to be written in the book. I would like to know which formula he talks about, although I ...
2
votes
1answer
739 views

Feynman Rules for massive vector boson interactions

I am stuck at the beginning of a problem where I am given an interaction term that modifies the regular QED Lagrangian. It involves the interaction between a photon field and a massive vector boson: ...
2
votes
2answers
223 views

numerical formulation of Dirac equation plus electromagnetic field

I have the following equations describing the electron field in a (classic) electromagnetic field: $$ c\left(\alpha _i\right.{\cdot (P - q(A + A_b) + \beta mc) \psi = E \psi } $$ where $A_b$ is ...
2
votes
3answers
966 views

If electromagnetic fields give charge to particles, do photons carry charge?

As I understand these two statements: An electromagnetic field gives particles charge A photon is a quantum of electromagnetic field It must mean that a photon carries charge. But I guess it isn't ...
2
votes
1answer
197 views

For someone who only studied electromagnetism, what is the modern way to explain electromagnetic fields?

After reading most of the electromagnetism chapters of Feynman's lectures on physics, I would like to understand in more detail, at least an idea, of what causes the electromagnetic fields. Not sure ...
2
votes
1answer
28 views

How does the electric field operator change inside an optical cavity

In the free field, transverse electric field operator is given by the below expression; $$d^{\bot}(R)=i \sum_{p,\lambda}\Big( \frac{\hbar cq}{2V\epsilon_{0}}\Big)^{1/2} ...