# Tag Info

## New answers tagged quantum-electrodynamics

3

There exists an extensive literature for discretization of the abelian and the non-abelian gauge theories, known as lattice QED and lattice QCD, respectively. Here we will only sketch the main idea. Let us for simplicity use Euclidean signature $(+,+,+,+)$. A small Wilson-loop $$\tag{1} W~=~{\rm Tr}{\cal P}e^{ig\int_{\gamma}A}$$ lies approximately in a ...

3

You should not imagine a virtual photon as an individual object wandering from one charged particle to another. This picture is simply inapplicable. Unfortunately, Feynman diagrams mislead people to imagine such things. Actually, Feynman diagrams are good for calculation and bad for imagination. Feynman diagrams have been introduced to help physicists to ...

1

All charged particles emit photons which are uncharged. They may, given the right boundary conditions. So how does the photon "know" that it's leaving one kind of charge and "lands" on another? What you are describing here is a "virtual photon", an interaction between two charged particles. There is the complicated way, i.e. mathematical ...

0

You can think of a photon as a quanta of energy. In that case, it can impart its kinetic energy to a charged particle, or, vice vers, a unit of energy can be released when a charged particles slows down and loses kinetic energy

4

There are, in general, no closed form solutions (aka formulas) for the spectra of multi-electron atoms. There are reasonably precise formulas for special cases, like approximate values of x-ray transitions from inner shell electrons, though. Unlike in case of hydrogen and Rydberg atoms, which can be treated as a non-relativistic one-body problems (i.e. for ...

0

Light changes direction when there is a switch in the medium through which it travels. For example, from air to water. Probably it is the density of the medium which matters. This is why you see waving images when looking over a hot car on a sunny day. If so, if one would create a sequence of progressively denser mediums, he could divert it considerably from ...

9

I'm a bit rusty on my qed, but I'll give this a shot. The simplest case would be described by a diagram similar to: But the $e^--e^--\nu_e$ vertex doesn't exist (also note that I can't draw the required arrow on the neutrino) - the vertices of the standard model (with the exception of vertices involving the Higgs and neutrino oscillations) are: With ...

7

The magnetic moment of the electron is a magnetic moment, so the right magnetic field around it is $$\mathbf{B}({\mathbf{r}})=\nabla\times{\mathbf{A}}=\frac{\mu_{0}}{4\pi}\left(\frac{3\mathbf{r}(\mathbf{\mu}\cdot\mathbf{r})}{r^{5}}-\frac{{\mathbf{\mu}}}{r^{3}}\right).$$ The world is quantum mechanical – and so is any viable description of the spin – so we ...

0

Until an expert in this field gives a rigorous answer to your question, I will give you my view. If I understand correctly your questions, you are on the one hand asking about other types of existing exchange interactions between virtual particles and real particles, and on the other hand you claim that using the usual virtual photon picture for the ...

1

To get a better understand of what is going on, take a look at the plot below, also linked here: http://en.wikipedia.org/wiki/File:Dispersion_Relationship.gif What the author meant by "letting the speed of light go to infinity" is that the we let the slope of the blue line become infinite. In that case, the solid red line would not curve as shown below, ...

3

Feynman diagrams are more than just the Lagrangian. They can be acquired by expanding the path integral of the theory into a perturbative series. There is a priori no reason to assume that all quantities needed in order to produce sensible results are consistent with gauge invariance. One possible issue is the problem of regularization: the way your ...

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