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

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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 ...
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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 ...
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What low-level process drives a frequency-doubling crystal?

I was reading about second-harmonic generation (SHG) crystals (or frequency-doubling crystals) used to produce green laser light from IR. What low-level process in the crystal is actually driving ...
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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 ...
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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 ?
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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 ...
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286 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 ...
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Vacuum polarization of dark matter candidates

Can a dark matter particle (axions, for instance, but the question applies to any valid candidate for dark matter) induce QED vacuum polarization effects even if being electrically neutral and with no ...
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204 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?
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252 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 ...
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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 ...
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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 ...
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'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, ...
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Under which representation of U(1) transform electron and photon gauge field?

I know that under $SU(2) \times SU(2)$, the left-handed electron transforms under $ ( \frac{1}{2},0 ) $ representation and the vector gauge field $A_\mu$ under $ ( \frac{1}{2},\frac{1}{2}) $. Since ...
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What is the value of the fine structure constant at Planck energy?

At low energy, 511 keV, the value of the fine structure constant is 1/137.03599... At Planck energy $\sqrt{\frac{\hbar c^5}{G}}$, or 1.956 $\times$ 109 Joule, or 1.22 $\times$ 1028 eV, it has a ...
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Dimensional transmutation in QED?

I am familiar with the QCD dimensional transmutation (QCD is dimensionless theory but via renormalisation we get dimensional parameter; we have to choose some referent scale...), but I'm not sure if ...
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Experimental proof of gravitational redshift of light

Has the gravitational red shift been proven for electromagnetic waves only or also for a single photon?
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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 ...
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Is there any relationship between Gravity and Electromagnetism? [duplicate]

We all know that the universe is governed by four Fundamental Forces which are The strong force , The weak force , The electromagnetic force and The gravitational force . Now, is there any ...
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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 ...
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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 ...
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Chiral anomaly and decay of the pion

I am told that if all classical symmetries were reflected as quantum symmetries, the decay of the neutral pion $$\pi^0 ~\longrightarrow~ \gamma\gamma$$ would not happen. Why would the conservation of ...
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582 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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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Coulomb interaction as virtual particles exchange?

I've been reading about virtual particle exchanges in physics books and in Physics SA posts, where a particle interpretation of gravity and Coulomb interaction is established. The Feynman Diagram ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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Angular momenta of photon

$A^\mu$ can have multipole expansions in classical electrodynamics. This gives rise to dipole photon, quadrupole photon etc. For dipole photon $j=1$ (In electrodynamics books they write it as $l=1$). ...
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some questions regarding Doppler shifting versus absorption-emission

I just got in what I thought was a silly exchange where a self-identified physicist states that the difference between "red-shifting" (in the Doppler sense) and the re-emission of light at longer ...
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Alternative methods to derive the static potential in the NR limit of QED

In QED, one can relate the two-particle scattering amplitude to a static potential in the non-relativistic limit using the Born approximation. E.g. in Peskin and Schroeder pg. 125, the tree-level ...
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Optical waveguide that can displace a 4D light field

Has anyone invented an optical waveguide that can "pipe" a scene from one place to another unaltered? More precisely, I want to displace (and/or rotate) a 4D light field. An optical waveguide is an ...
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Will an entangled idler electron induce a current in a conductor if the signal elctron's spin is measured?

I'm assuming a hypothetical setup as follows: Two labs (Alice and Bob) exist. Each has one electron of an entangled pair. At Alice, the electron travels through free space towards a magnetic field of ...
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what is the relationship between the dynamical casimir effect and virtual particles?

Since virtual particles are disturbances in a field, and not particles in any sense, as explained here, how is it that true photons arise from them when excited with kinetic energy via the dynamical ...
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Is there a point interaction model of the electron?

Is there a point interaction model of the electron? Is there a point interaction model of the electron? I imagine something like $\propto(\bar \psi\psi)^2$ (edited). Is such a thing in use? Since I ...
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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 ...
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Back-of-the-envelope calculation of electron anomalous magnetic moment

I wonder if there is an intuitive way to obtain the $\frac{\alpha}{2\pi}$ correction to electron's $\frac12 (g-2)$ just like how Bethe estimated the Lamb shift? Here is an attempt by Drell & ...
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Electromagnetic force interaction

As far as I know, the electromagnetic force only interacts on particles with electrical charge, but I was told that the electromagnetic force was involved in the following reaction: ...
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Electron propagator in a strong background B field

Near a magnetar with $B>B_\rm{QED}$, the strong B field will suppress the Compton scattering cross section of photons with a specific polarization (E-mode). Some references I know deal this problem ...
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Difference between positron and electron scattering in Coulomb field

In first order of perturbation theory the S-matrix amplitude for electron scattering in the Coulomb field will be (up to normalization factors) $$ S_{fi} = \frac{iZ q^2}{\sqrt{2E_{f}2E_{i}}}\bar ...
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How do photons decay in superconductors?

If $A$ is the vector potential, the London equations imply that: $$(\nabla^{2}-\mu^{2})A=0$$ if there is no external current. This can be interpreted as an effective photon mass and so, light ...
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Equivalence between different formulations of QED

I have looked at Greiner's book on QED, where he uses the Feynman propagator approach for QED. He solves a lot of things and calculates several processes without "second quantisation" (and without ...
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If the measurement of the proton size is correct and it is lower that it was expected than what are the theoretical implications?

In the press release of the recent measurement of the proton structure, they barely mention various theoretical explanations for the effect. What is the most likely (not assuming now that the ...
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How does this paper relate to standard QED?

This paper proposes a microscopic mechanism for generating the values of $c, \epsilon_0, \mu_0$. They state that their vacuum is assumed to contain ephemeral (meaning existing within the limits of ...
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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 ...