Qed Definition and 324 Threads

Hi! In e+/e- to mu+/mu- scattering, if the initial electron/positron radiates a photon, then I have an IR divergence. How do I treat it?

Hi In cQED and the Jaynes-Cummings model, three parameters are usually introduced which describe the atom-cavity system: The radiative lifetime γ, the cavity linewidth κ and the pure dephasing rate 1/T2. However I am not that familiar with the latter parameter. Basically I guess it describes...

Hi! I'm trying to learn the Feynman rules trough Wick's theorem right now and I'm focusing on QED. Here the first order term of the S-operator can be written as -ie\int d^4x :\bar \psi(x) \gamma^\mu \psi(x) A^\mu(x): but the author of the book I'm reading (Greiner Reinhart) claims that all...

It seems to be a dumb question. But I haven't seen anyone making this connection between QED and Classical EM in a complete fashion. The only example I've seen is the connection between two particle scattering amplitude calculation in QED (Peskin's book), and the amplitude of a particle...

I recently read somewhere that the predictions of QED in the classical limit haven't been nearly as well-studied as, say, the classical limit of quantum mechanics. This is a little confusing: doesn't QED just reduce to Maxwellian electrodynamics with additional small nonlinear quantum...

Hi All, I am currently undergoing independent study in quantum mechanics with Zettili's "Quantum Mechanics: Application and Concepts" and would like to know some good books for independent study for the "next level". My ultimate goal is to end up on the forefront of physics in terms of...

I understand that an electron gets its mass by self-interaction of its fields which is explained by QED, but on the other hand there is the higgs mechanism which gives mass to all the fundamental particles. Does the electron have two types of mass one which is due to the QED mechanism and the...

The standard layman description of QED is that forces are no longer mediated by fields present at all points in space, but by particles that are (presumably?) at least somewhat localized, and carry some energy. Forces are then exchanged between two electrons by "exchanging photons" -- at the...

; Can someone explain to me (in layman's terms,) how it might be possible to associate the interactions of the up/down quarks in the strong nuclear force as analogous to the way electrons and photons interact in quantum electrodynamics ?

According to Wiki: "If a beta function is positive, the corresponding coupling increases with increasing energy. An example is quantum electrodynamics (QED), where one finds by using perturbation theory that the beta function is positive. In particular, at low energies, α ≈ 1/137, whereas at...

Many of you stated how ad hoc is QFT as the field is supposed to be non-interacting yet how could they get an incredibly accurate value of calculated magnetic moment of the electron of value 1.0011596522 compared to measured 1.00115965219 with accuracy to better than one part in 10^10, or...

Hi Does anybody know of a good book on cavity QED? It seems that most books only have a small part of a couple of pages covering the subject. Niles.

Please teach me this: Why we do not consider the divergences in loops in QED when p^{2}→m^{2} but only consider the soft photon when k^{2}→0(IR divergence) and UV divergence? Thank you very much in advance.

Hi all, I am looking for some more information about the experiments that Feynman describes during the lectures that he gave in Auckland which can be viewed on the vega science trust website. The first experiment is where photons are transmitted or reflected by one surface with a second similar...

I did some perturbative calculation earlier, and it seemed I have to impose angular momentum conservation by hand, or else I couldn't get the desired result. We know angular momentum must be conserved finally, but is it conserved at every order in Dyson series?

I'm trying to think of real-world applications of the standard model of particle physics, but can't come up with anything. Are there any technological applications in which neither non-relativistic quantum mechanics nor Dirac's relativistic wave mechanics is insufficient, and QED must be used...

Suppose we were to simulate 1D QED on a 1D lattice. How much information do we need at each lattice site given the mass, charge, and spin of the particles (does spin make sense in 1-1D spacetime?)? The links between lattice sites represent the gauge field? How much information is needed at...

I presented a way to derive Coulomb force via the canonical mechanism. One uses Coulomb gauge \partial_i A^i = 0 derives \Delta A_0 = -4\pi\,\rho which can be inverted formally A_0 = -4\pi\,\Delta^{-1}\,\rho and calculates the interaction term in the Hamiltonian density...

AAAD QED = Action-At-A-Distance QED Simple question: is AAAD (= Action-At-A-Distance) QED standard / mainstream physics - or beyond standard? http://rmp.aps.org/abstract/RMP/v67/i1/p113_1 See here: https://www.physicsforums.com/showthread.php?t=551928

I picked up a copy of Feynman's QED - "A strange theory of light and matter" from the university library today because it looked interesting and I was wondering if this book is still relevant to todays Quantum physics? It's a fascinating read but I want to make sure I am not learning stuff...

Hi there - does anyone know a good reference in which it is shown that we can derive QED from the Weinberg-Salam model? (Or if we can't, does anyone know why?) Thanks!

Am interested in grad level QED textbooks. Any recommendations appreciated. Also, what are the latest papers on the subject? What journals should I try to get access to? Thanks.

Hi, excuse the funny title :). In his book on quantum field theory Zee says (pag 245, fouth line) that QED gauge symmetry follows from the conservation of the current j=ψ γ^μ ψ (with the bar on the first spinor). I'm confused because that current is the noether current resulting from the...

Please teach me this: It seem to me that when we consider high momentum,then the strong interaction become asymtotic week force,so we can use perturbative QCD.But at the same time,when considering large momentum,the ''electric charge'' became large,then the ''electric force'' between quarks...

First off, I am very ignorant to this subject. I am only a rising sophomore in physics and have not taken any "modern" physics courses yet(but will in the fall). So I have heard/read that quantum electrodynamics is the more accurate scientific theory to date. Is this theory "complete"? It...

I'm starting to read up a bit on QFT, starting with Griffith's intro to elementary particles book. I've gone through the background stuff and I'm now into the QED chapter. I was trying to get a feel for how the number of loops introduces free momentum variables, and I ended up drawing a diagram...

I tried asking a similar question earlier, but based on the answers I got I wasn't able to convey myself well. Here's Feynman's argument (at least as I understand it) for why, from a Quantum perspective, light (roughly) travels in straight lines from points A to B: 1) the photon will travel...

Hi all, I'd like to improve my understanding of classical electrodynamics, but as a UK PhD student my time for self-study is pretty limited- we don't make much time for general physics education at a graduate level. I was wondering if someone could recommend a short path through Jackson's...

Quantum Electro Dynamics, the quantum theory of the photon, describes the photons interaction with electrons and this is what I beleived created the electromagnetic field. However recently I've heard a disscusion that virtual photons and their interaction with electrons and the polarization of...

I'm reading Feynman's QED, which is a nontechnical overview of quantum electrodynamics. In this book Feynman makes three claims that I am curious about. I have a math background but regrettably not much in physics. 1. Light is a particle, period. It's not true that light is "sometimes a...

Hi, I was wondering whether the decay of the Pi-0 meson in QED to an electron positron pair can occur as follows: Pi-0 -> virtual photon -> e+e- or does it have to go via Pi-0 -> two virtual photons -> e+e- (the Feynman diagram has a 'square' of virtual electrons/photons)? I have...

A few days ago I started reading through Feynman's QED. It is a very good book, I am very much enjoying it. There's something I don't understand. When Feynman starts to talk about why light is reflected such that the angle of incidence equals the angle of reflection, he gives an example where...

Hi! I'm studying an introduction to QED and I don't understand the bosonic propagators. Consider the electron/positron scattering with the exchange of a virtual photon. According to perturbation theory, the propagator is: T=<f|H|i>+\sum<f|H|n>\frac{1}{E_i-E_n}<n|H|i>+... where f is the final...

Homework Statement I want to check that the QED lagrangian \mathcal{L}=-\frac{1}{4}F^{\alpha\beta}F_{\alpha\beta} + \bar\Psi(i\displaystyle{\not} D - m)\Psi where F^{\alpha\beta} = \partial^\alpha A^\beta - \partial^\beta A^\alpha, \ D^\mu = \partial^\mu - ieA^\mu is invariant under charge...

Hi, I know QED is one of the most tested theories in all of science (and one of the most accurate) but I wanted to know if it disagreed at ALL with its predicted values of both http://en.wikipedia.org/wiki/Fine_structure_constant http://en.wikipedia.org/wiki/G-factor_(physics ) The thing...

I've been studying GR for 2 semesters now and am about to dive into quantum mechanics and so I thought it appropriate to ask this question. Why is it that Quantum theory and GR don't interlap at quantum scales? More generally, why doesn't QED fit into GR? fundamental concepts as well as specific...

Hi, I have been deriving the renormalisation constants in QED as part of my project. I have been using Peskin and Schroeder. I am a bit confused with a couple of things and was wondering if anyone could please help! Firstly, why do we chose not to absorb the Z_3 constant in the electron...

I'm just beginning to learn about Feynman diagrams and wanted to make sure I've got the correct basic understanding of QED. This is what I believe to be true right now: QED allows us to describe the interaction between an EM field and light/matter. The QED vertex is composed of a photon and...

Hello all... I confess, I didn't make much googling about this, so if this question is already answered :) just show me the link to answer... In his famous video lectures about quantum electro dynamics, Richard Feynman is talking about electron and photon functions E and P. And whole...

OK guys Can anyone tell me some hot research problems in theoretical quantum optics/cavity QED right now ?

Hi, I have been looking at the renormalisation of QED and been using Peskin & Schroeder. I understand (I think) what is going on, but I am slightly confused over 2 issues: 1. In the new feynman rules from the counterterms, the feynman diagrams all have a small circle with a cross in...

Hello, I don't understand two steps in solution to the problem: I. Homework Statement Show that QED action is invariant under gauge transformation. II. Relevant equations QED action: S= \int{d^{4} x \left[\overline{\Psi}\left(i\gamma^{\mu} D_{\mu} -m \right)\Psi...

hi i heard some things about quantum electrodynamics and one thing was that they gave up the concept of actual fields and said that the electromagnetic information from one particle to the other is transported by photons. Now my question is: Can one observe these photons or is it just a...

SR and QED: how? how the particle moving at a speed near to that of light interact to it's surrounding,considering the very fact of it's time dilation? what i mean to ask probably is that will it b possible for this particle to create another one from it's energy and still manage to throw...

I have a question concerning renormalization of QED. I don't know if Feynman diagrams with counterterms on ecternal legs are allowed. Normally to find S matrix amputated green function is necesary and to find it one don't take into account all propagators on external legs - they are canceled...

does anybody know a book, where the compton-scattering with respect to the initial photon-polarisation is calculated? (beside landau-lifschitz-berestetzki)

Supposed external energy is added to the system such that the electron is rise to the next orbital releasing photon. Can QM still be used to model it or does one need Quantum Field Theory? How about additional external energy that increase say the molecular rotational or translational speed, is...

QED: the strange theory of light and matter. " Light is made of particles " ? Over Christmas I ordered the book: QED: The strange theory of light and matter by Richard P feynamn 2006 edition. Note: This book was written in 1985. "We know that light is made of particles because we can't...

HI everybody. I'm here with a question that I would like to discuss with you. As you all probably know better than I do, in classical electromagnetism there exists the so called "Runaway solution", i.e. the auto-acceleration of a charged particle. It is not clear to me how this problem can...

In QED calculations are made with variable c. But Duff says that c does not exists, because it is only a transformation factor. So if we put c=1 how QED is changed at small distances?