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 the exact meaning that QED perturbative series is only asymptotic and eventually diverges at very high orders?

When I read paper PRB89, 235431 about the effective field theory of graphene, there is a statement that QED perturbative series is only asymptotic and eventually diverges at very high orders (e. g. ...
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What is the exact mechanism in line broadening of transition frequencies?

I've been having trouble understanding why transition lines in unperturbed states are not infinitely narrow. I'll run through my reasoning and hopefully that helps find the flaw. I imagine that if we ...
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Quadratic terms in QED lagrangian density

I recently learned that when we speak about a "free lagrangian", this actually means that the lagrangian is quadratic in the fields. When considering the Lagrangian density describing the coupling to ...
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spin direction of the electromagnetic field tensor

I guess the electromagnetic field strength tensor $F_{\mu\nu}$ can be considered as a spin-1 field. So, is it possible to derive $F_{\mu\nu}$'s spin direction based on the elements in the tensor (the $...
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Equal-time commutation relations, Feynman propagator for gauge parameter $\lambda = 1$, physical meaning

Classical electromagnetism (with no sources) follows from the actions$$S = \int d^4x\left(-{1\over4}F_{\mu\nu}F^{\mu\nu}\right),\text{ where }F_{\mu\nu} = \partial_\mu A_\nu - \partial_\nu A_\mu.$$The ...
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Maxwell equations and quantized electromagnetic field

When the electromagnetic field is quatized for a single mode, we first take Maxwell equations and proceed to write the electric and magnetic field as a stationary wave, since we consider the ...
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Would the detection of advanced waves be possible in curved space-time?

In the transactional interpretation of quantum mechanics reference 1, inspired by the Wheeler–Feynman absorber theory, a transaction is formed between the emitter and absorber by a superposition of ...
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Does orbital angular mometum has no meaning for single photons?

In the quantization of free electromagnetic field, it is found that the left-circularly polarised photons corrsponds to helicity $\vec{S}\cdot\hat p=+\hbar$ and right-circularly polarised photons ...
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How to describe time evolution in relativistic QFT?

I must confess that I'm still confused about the question of time evolution in relativistic quantum field theory (RQFT). From symmetry arguments, from the representation of the Poincare group through ...
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Lagrangian for $\mathcal{N}=4$ SQED in 3D

What is the Lagrangian for $3D$ $\mathcal{N}=4$ supersymmetric QED, with $N_f$ hypermultiplets? In particular, which is the form of the Fayet-Iliopulos terms, and the real mass terms?
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What are skeleton diagrams and what is their use in qft and many-body physics?

How does one construct skeleton diagrams from specific Feynman diagrams (e.g. for the electronic Green function in QED and in many-body gases, for the polarization function, for the vertex function, ...
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Interpretation of the electromagnetic field strength tensor as a spin-1 field

If I understand correctly the electromagnetic field strength tensor $ F_{\mu\nu}$ could be considered as a spin-1 field. In that case, what can one say about the total spin and the $z$-component of ...
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Does a Description with Photons as Force Carriers Apply for Non-Radiative Systems?

What is the full quantum mechanical description of the statement from classical electromagnetism "the electric field of a uniformly charged infinite flat plane is constant"? By "full" I mean that I'm ...
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Lorentz structure of coupling in QED

what is meant by the "Lorentz structure of the coupling in QED" as a possible test for QED?
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How photons can emerge quantized if their cause is continuous?

I know that photons are quantized, they are not continuous. But they are created by an accelerated charge. So how is it possible to have a quantized outcome from a symmetric continuous event? I mean ...
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Peskin-Schroeder, Unitarity of the S matrix, eq 9.61

I have a question regarding a derivation in Peskin and Schroeder's QFT book. On page 298, he is discussing a method for defining a gauge invariant S matrix. He does this by defining projection ...
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Can photons move in circles?

A photon can travel between two points A and B in a straight line. However, there is a chance it will go in a slightly curved path. Is there a chance the photon will turn around? Does this mean that ...
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If a photon doesn't necessarily travel in a straight line, doesn't it defy the law of cons. of momentum?

I just finished reading Richard Feynman's lectures on Quantum Electrodynamics (QED: The Strange Theory of Light and Matter) and it fascinated me. However, there's an unanswered question I have from ...
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What is going on in the photon-photon scattering Feynman diagram?

I understand the basic concepts of a Feynman diagram, but I don't get what is going on here. I have named the photons ABCD and the fermions 1234 for clarity. I'm going to assume that the vertical ...
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When does the concept of electric field in classical electrodynamics fail, and QED is needed?

It is really hard to find reference to when the traditional concept of electric wave, especially TEM wave, fails, and needs to be replaced by quantum electrodynamics. So when does the concept fail? ...
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Dipoles in an external rotating field?

Consider a bunch of magnetic dipoles in $x-y$ plane in an external magnetic field $B(t)=B_0 \hat{z}+B_1(\cos\omega t~\hat{x}+\sin\omega t~\hat{y})$. The dipoles are rotating around $z$ axis and of ...
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Polarization Sums in QCD for the calculation of parton model splitting functions

Before i state the actual problem, here's a premise. In the case of a Spin 1 massive particle it's possible to demonstrate that $$\sum_{\lambda=0,\pm1}\epsilon_{\lambda}^{* \ \mu}\epsilon_{\lambda}^{\...
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Electric field operator in 2D geomatry

In the free field (3D), transverse electric field operator is given by the below expression; $$e^{\bot}(\textbf{R}) =i \sum_{\textbf{p},\lambda}\Big( \frac{\hbar cp}{2V\epsilon_{0}}\Big)^{1/2} \{e^{(\...
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Why don't photons split up into multiple lower energy versions of themselves?

A photon could spontaneously split up into two or more versions of itself and all the conservation laws I'm aware of would not be violated by this process. (I think.) I've given this some thought, and ...
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QED+Classical Background Renormalization

I would like to ask a question related to quantum corrections and renormalization in QED. We have the QED vertex $\overline{\psi}[-ie \gamma^{\mu}(B_{\mu}+A_{\mu})]\psi,$ being $B_{\mu}$ a classical ...
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What happens to Hydrogen-Boron plasma at 3 billion Kelvin?

A recent popular report states (beware, I believe it is not peer reviewed and this slightly smells like a PR stunt) that a private company TriAlpha has made some notable progress towards Hydrogen-...
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Why do electrons and positrons exhibit opposite helical motion in a magnetic field?

When you throw an electron through a solenoid, it moves helically around the field lines, as per this schoolphysics illustration: © Keith Gibbs 2013 Then if we were to throw a positron through the ...
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How far do the propagation paths in QED go?

I am currently reading Feynman's popular book on QED "the strange theory of light and matter". I know classical optics quite well, know about Fresnel, Brewster angle and the like. I also am now used ...
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$U(1)$ local gauge invariance in QED [duplicate]

While constructing Lagrangian of QED, we don't add the mass term for photon $\dfrac{1}{2} m^{2}A_{\mu}A^{\mu}$ because gauge invariance does not allow. I want to ask, whether "$\bf{Theoretically}$", ...
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Two questions about Feynman propagator

Taking for example the meson propagator: $$ \Delta_F (x-y) = \int \frac{d^4k}{(2\pi)^4} \frac{e^{-ik(x-y)}}{k^2 - m^2 + i\epsilon}. $$ It describes a meson that propagate from a point of Minkowski ...
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Observing a photon during flight

When I was reading about the double-slit experiment in quantum mechanics, everything seems to make sense in terms of the waves and the interference pattern, but if thinking more about this observation,...
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Does a charged particle propagating in free space have a 'self-energy' like term due to it’s interaction with the fluctuations of the quantum vacuum? [closed]

Does a charged particle propagating in free space have a 'self-energy' like term due to it’s interaction with the fluctuations of the quantum vacuum? (particle-antiparticle pairs popping into and out ...
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What's actually going on when light interacts with matter?

There are many different theories but all of them fail to explain all 3 phenomena of light(absorption,emission,transmission). https://www.youtube.com/watch?v=CiHN0ZWE5bk https://www.youtube.com/...
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Electromagnetic wave and quantum mechanics [duplicate]

I'm very new to physics. I studied and read about quantum mechanics and what the assumptions are (wave particle duality, uncertainty principle, observation, wave function collapse, etc.), but I also ...
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Why photons reflect off glass?

Why photon reflects and refracts through glass? Some photons pass through glass and some reflects.I know this is due to energy levels of electrons of glass, an incoming photon is unable to excite the ...
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Ramsey pulse versus optical pumping: what's the difference?

A Ramsey pulse is a coherent process, where the electronic states of for example an ion (or some other two-level-system) are coupled to a laser field. By tuning the laser precisely, we can coherently ...
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How light splits up into different colours when passed through prism using QED?

I want to know how light gets splits up into different colours when it is passed through prism? How light interacts with atoms and electrons of the prism? Can someone explain this to me using Quantum ...
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What actually happens when light meets a surface(QED or QM or Condensed matter physics)?

I want to know what actually happens when light meets a surface like water or wood. Quantum mechanics says that objects are neither "transparent" nor "opaque". Rather a system as a whole can accept "...
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How is the EM force exchanged over long distances?

The Situation Imagine we place two charged objects a very far distance apart, essentially making them point charges. How does the EM force interact between the two point charges if virtual photons ...
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How to choose the proper loop correction?

I review my QFT lecture notes and I am having hard times to figure out the significance of Ward identity in vacuum polarization. In class, we calculated one loop correction stated as $$ i\Pi^{\mu\...
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How Ward Identity indicate vacuum polarization correction?

In Peskin & Schroeder Chapter 7.5 Renormalization of The Electric Charge, they mention that vacuum polarization correction is $$ iM= (-ie)^2(-1)\int_{}{}\frac{d^4k} {(2\pi)^4}Tr\bigg[\gamma^{\mu}\...
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QED and anomaly

I've just started to learn anomalies in quantum field theories. I have a question. How to show that QED is free from vector current anomaly and what would happen if it were not? In other words, how ...
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Principle of superposition and QED

For finding a net force on a charge when it is in influence of many charges we simply do vectorical addition of all individual interaction of that charge with others. That's what is principle of ...
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Can QED explain this or do I have revert to the classical model of light?

I want to know can QED can explain this image,like why there are someplaces with low light (shadows) like behind the chair, and why there are some places that are bright(rest of the floor). I know ...
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Quantising the magnetic monopoles the make Maxwell symmetric

I don't believe this has already been asked, but I might be wrong; sorry. One can add a magnetic charge density/magnetic monopoles to Maxwell's equations to make the theory symmetric between the ...
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What happens to theoretical physics if a photon has non-zero mass?

I want to know the theoretical implication if photons have a non-zero mass. What happens to the Maxwell equations? What happens to QFT? If the photon have mass it can decade?
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Phase on Aharonov-Bohm effect doubts

How I show that $$\Lambda(\textbf{x}')=\frac{q}{\hbar}\int \mathbf{A} \cdot d\mathbf{x'}$$ on $$ \tilde{\psi}(\textbf{x}',t)=e^{[\frac{iq\Lambda(\textbf{x}')}{\hbar c}]}\psi(\textbf{x}',t)$$ for ...
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Compton Scattering Feynman diagram integral expression

I'm trying to write down the integral expression according to the feynman-rules for this Diagram of an electron with compton scattering and a one-loop correction: ![Compton Scattering][1] $$(-ie)^4\...
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Current density defined by the scattering operator

I have a problem with the definition of the current density. In most literature it is defined as $j^\mu=\frac{i}{2}(S^*\frac{\partial S(A)}{\partial A_\mu(x)})$. I understand that normally we use ...
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What is $\mathcal{N}=2$ QED?

I would like to know is $\mathcal{N}=2$ QED is simply a $\mathcal{N}=2$ theory with gauge group $U(1)$ like in normal QED? If not, exactly what theory is it? Is there some reference for it?