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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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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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 ...
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753 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: ...
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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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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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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 ...
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30 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} ...
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Can we measure the electron spin independently of its magnetic moment?

What experimental evidence do we have for the intrinsic angular momentum of the electron (its spin)? I am specifically interested in whether we have a value for this that is independent of the ...
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68 views

The contraction of fermion field in 1+1-dimensional massless QED

My question comes from the textbook by Peskin & Schroeder, the integral (19.26): $$\begin{align} \int \frac{d^2 k}{(2\pi)^2}\! e^{- i k\cdot (y-z)}\frac{i \not{k}}{k^2} = -\not\partial ...
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Counting d.o.f. and gauge fixing $A_{\mu}$ and $\psi$ in $D$-dimensions

Setup: Let us assume we are in $D$-dimensional Minkowski space-time where $D=d+1$. Consider a free Abelian gauge theory. Then the electromagnetic field will satisfy $$\partial_{\mu}F^{\mu \nu}=0 ...
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Linear and circular polarization in quantization of the EM field

I am going through the "Quantization of the EM field" in Chapter 7 of Sakurai's Modern Quantum Mechanics, which basically goes like: The vector potential satisfies wave function $\nabla^2\mathbf ...
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How do two electrical charged particles know to repel or attract each other?

Now per QED, electrical charges interactions are effected by photons. Suppose you are one of the two charges. How do you know to attract or repel the other charge? In other words, how do you know if ...
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126 views

What are hot electrons?

What are they? How are they created? And what do they have to do with plasmons? I searched the web, but I would like more reliable and straightforward sources.
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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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Admixtures of longitudinal and timelike photons!

In the quantization of electromagnetic field the physical states $|\psi\rangle$ are found to obey the following relation: $[a^{(0)}(k)-a^{(3)}(k)]|\psi\rangle=0$ It is explained as the physical ...
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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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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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568 views

Does a quadrupole transition mean emission of one photon with spin 2?

If it's true and spin-2 photons do exist, could you please point to some literature that discusses spin-2 photons? If not, then how exactly does a selection rule for quadrupole transition make sense ...
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285 views

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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158 views

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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47 views

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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108 views

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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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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How do I calculate a Feynman diagram with one loop?

I'm following Peskin & Schroeder and I'm trying to calculate the momentum space representation for the following diagram, Q4 in this link. Paper The loop is what's causing me problems. I'm not ...
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Thomson scattering on the elections does not produce any circular polarization?

All references on CMB polarization has this statement as if it is a trivial fact. But I have to admit that I completely don't understand what this sentence is telling us.
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Charge operator for Dirac spinor

In QED, the gauge transformation which acts upon a fermionic field $\psi$ is $$\psi'(x)= e^{i \alpha(x) Q}\psi(x)$$ where $Q$ is the charge operator. Most of the time it's just written as $$\psi'(x)= ...
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Time ordering, interaction Lagrangian calculation, QED

I am trying to compute $$ \langle 0| \, T\left\{\phi^\dagger(x_1) \phi(x_2) \exp \left[i \! \int{L_1(x) \, \mathrm{d}x} \right] \right\}|0 \rangle $$ for $$ L_1(x) = ...
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Intuition behind $U(1)$-gauge model of Electrodynamics in a general spacetime

As the article Electrodynamics in general spacetime greatly explains, the $U(1)$-gauge theory is a good base for working in non-simply connected spaces. But I wonder whether there is a deep reason to ...
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103 views

Photon polarization sum prescription in $e^-e^+\to{}2\gamma$

In calculating the amplitude for the process $e^-\gamma\to{}e^-\gamma$ the substitution $\sum\epsilon_{\mu}\epsilon^*_{\nu}\to-\eta_{\mu\nu}$ is useful to sum over photon polarizations. If we ...
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Non-minimal coupling (Pauli Coupling) of gauge field with a non-relativistic scalar field

I am wondering if it makes any sense to non-minimally (say, Pauli-like) couple an external gauge field with a non-relativistic scalar field: \begin{equation} p_\mu \rightarrow p_\mu - e A_\mu + ...
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Electromagnetic reaction force?

The classical (retarded) Lienard-Wiechert scalar and vector potentials describe the electromagnetic field due to an arbitrarily moving electric point charge. Thus given the motion of electron $A$ one ...
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Are all positrons electrons traveling back in time?

I have recently read Richard Feynman's "QED" and in it Feynman describes positrons as 'how we view electrons when they are going back in time and we are stuck traveling forwards in time'. I was ...
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Convergence of light by light scattering amplitude

Perhaps I'm too exhausted to see the answer of why the photon-photon scattering should contain no divergences. In Peskin and Schroeder page 320 we find that because of the Ward identity the ...
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Feynman propagator with general $\xi$ parameter

Hey from my notes in my PS book it seems I have solved this some time in the past, but I cannot seem to get the indices straight this time around. So in deriving the Feynman photon-propagator which ...
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Can the rate of virtual pair production from vacuum be computed?

Consider for instance the QED Lagrangian. Is it possible to compute the rate of virtual electron-positron creation from the vacuum?
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Expectation value for the time of a photon reflection

A photon is reflected by matter (by an electron in empty space). How long does the reflection take? (i.e. is there any infinitesimal time elapsing during the reflection process?), or more precisely, ...
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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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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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Nonlinear refraction index of vacuum above Schwinger limit

This question is more about trying to feel the waters in our current abilities to compute (or roughly estimate) the refraction index of vacuum, specifically when high numbers of electromagnetic quanta ...
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97 views

After quantization of electron vibrations, do we need electrons anyway?

The title question is not ment in a general context, but one in which goes to the plasmon theory. In that case, how is are the statistics (boson vs. fermions) of plasmons determined? And is there an ...
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Are electromagnetic “plane” waves measurable or just a virtual concept?

I find plane waves are uncompatible with light cone. Perhaps plane waves are "virtual" and can never be measured in that case, shouldn't we call plane waves as "virtual plane waves"? (other option ...
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Neutrino and electromagnetic forces

I learned from Wikipedia that neutrinos "are not affected by the electromagnetic forces". How was this identified experimentally?
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Electron-positron scattering: why is this the only diagram?

This is probably a very basic question, but I've been going through all my course materials and looking through various books to find a simple way of figuring this out. But consider the following ...
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Spectral series' formula of a given atom (other than hydrogen-like)?

The hydrogen spectral series is given by the Rydberg formula: The energy differences between levels in the Bohr model, and hence the wavelengths of emitted/absorbed photons, is given by the ...