Qed Definition and 324 Threads

Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065

Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065

Copyright reserved to Prof. Tripathy and NPTEL, Govt. of India. Duplication prohibited. Lectures: http://nptel.ac.in/courses/115106065/ Syllabus: http://nptel.ac.in/syllabus/syllabus.php?subjectId=115106065

I'm talking of the virtual EM modes of vacuum...

I know little about QED, QCD, and whatever the corresponding theory for the weak force is, and of course virtually nothing about the quantized theory of the gravitational force, which mostly doesn’t exist, so the following arguments and questions may be somewhat wrongly based where they refer...

I'm trying to understand renormalisation properly, however, I've run into a few stumbling blocks. To set the scene, I've been reading Matthew Schwartz's "Quantum Field Theory & the Standard Model", in particular the section on mass renormalisation in QED. As I understand it, in order to tame the...

In all Quantum Physics experiments, the sequence of measurement results is inherently random. Consider just the position observable. In the Schrodinger picture of non-relativistic QM, in each measurement-event, nature steps in and randomly selects one of the observable's eigenvalues/vectors to...

Hi, I've just started studying Feynman's thesis and am in need of some discussion regarding the three principles he put forward on the development of his 'Principle of least action in quantum mechanics'. The three principles are 1) The acceleration of a point charge is due to the sum of its...

What do you think of the following paper about QED? https://journals.aps.org/prd/pdf/10.1103/PhysRevD.96.085002 Infrared divergences in QED revisited Daniel Kapec, Malcolm Perry, Ana-Maria Raclariu, and Andrew Strominger Phys. Rev. D 96, 085002 (2017) – Published 10 October 2017 It has been...

The prefix is a bit irrelevant This is on renormalisation. How do they cancel out? Isn't it adding? So the mass experimental = m + (c2correction) so how do you cancel out the m and correction? I'm new to this area (just finished watching lectures by Richard Feynman, specifically a 4 lecture...

My aim is to derive the photon propagator in an Coulomb gauge following Pokorski's book method. In this book the photon propagator in Lorenz gauge was obtained as follows: 1. Lorenz gauge: ##\partial_{\mu}A^{\mu}=0## 2. It's proved that ##\delta_{\mu}A^{\mu}_T=0##, where...

I'm reading the book Quantum Field Theory and the Standard Model by Matthew Schwartz and currently I'm studying the chapter 17 titled "The anomalous magnetic moment" which is devoted to computing the corrections due to QFT to the g factor. My main issue is in the beginning of the chapter, where...

It is claimed that QED could predict certain quantities, like the lamb shift and magnetic moment of electron with astonishing precision of 12 digits. My question is the following: does QED predict only a few things to this precision, or does it predict, this precisely, the entire arbitrary...

Apologies if my question is confused, because I'm beginner in field theory: adding up all corrections, can we talk about an effective (at least approximate) overall mass-to-charge ratio for the electroweak or QED vacuums? Suppose we want to talk about the relative strength of...

Does anybody have more insights regarding https://www.nature.com/articles/ncomms15484 High precision hyperfine measurements in Bismuth challenge bound-state strong-field QED Does this really challange QED? Or does this mean that we miss certain contributions to QED calculations? The authors...

I have heard a virtual phton as used in QED defined as being forced carriers between two fermions which last for very short periods of time. A couple of questions about this: 1) how do we know these are photons and not some other force carrier if we cannot detect them directly? 2) can...

Hello, I know QED and QCD as isolated theories but now I thought about particle interactions with QED and QCD processes (like fpr proton-antiproton scattering). But I'm not sure how to interpret this mathematically. As I understood my Feynman diagrams are nothing more like pictures for the...

Hi. I'm at the second year to get my bachelor degree in physics. I actually know the fundamentals of physics. I was looking some threads on PF, then I found this one https://www.physicsforums.com/threads/is-qed-nonrelativistic.900451 My question is, given that I have approximately the knowledge...

I am reading Feynman's book QED: The Strange Theory of Light and Matter". What I am getting out of this is that a photon is like a tiny harmonic oscillator traveling through space. Each harmonic oscillator has frequency and phase. If two photons have the same source and start out nearly in...

One of the Feynman rules of QED is the following: For a closed fermionic loop, the Feynman rule is to start at an arbitrary vertex or propagator, follow the line until we get back to the starting point, multiply all the vertices and the propagators in the order of the line, then take the trace...

Hello, Apologies if this has been asked before. After watching Feynman’s QED lectures on the probabilities of different paths that photons can take towards a photomultiplier, a few questions came up in me. Let’s take the simple scenario in which a photon emitter is faced straight towards a...

[Mentor's note - this thread was split off from https://www.physicsforums.com/threads/a-skeptics-view-on-bohmian-mechanics.899967/ as it is interesting in its own right and a digression there] This is a distortion of facts. One looks at lattice QCD only because it is derived from the Poincare...

For centuries, scientists argued whether light was waves or particles. Light scattering with other light would favor the particle concept. Today we know both models are wrong, but quantum electrodynamics also predicts this scattering - just with an incredibly tiny rate, so it has never been...

Hello! I read today about the screening in QED and vacuum polarization. And the image they used to explain it was an electron surrounded by a ring of positrons and then by a ring of electron, which makes sense. Now, the Gauss's law outside and inside the 2 rings will give the same result, as the...

Hello, Reading Richard Feynman’s book “Quantum Electrodynamics” (Edited by Advanced Book Classics), I read that the electron’s self-energy is infinite and that has been a trouble for QED during 20 years. Feynman proposed a solution based on a cut-off, but that’s not fully satisfactory and I...

I've read that the photoelectric effect cannot be explained according to Maxwell's equations and theory of electromagnetism. Classical EM theory treats light as a wave and states that the intensity of the light matters and not the frequency. According to Einstein, if we think of light as a...

In Peskin and Schroeder problem 10.1 is about showing that superficially divergent diagrams that would destroy gauge invariance converge or vanish. We are supposed to prove it for the 1-photon, 3-photon, and 4-photon vertex diagrams. Does this change for scalar QED?

Although mass-less, a photon, like any other quantum particle, has a frequency/wavelength associated with its energy/momentum. If we have a group of photons all with the same specific energy, then each photon can be represented by a little, complex-valued plane wave. Photons are also EM waves...

I have the opportunity to pursue a research project in either lattice QCD or QED. In the case of QED, I'd be writing the code myself, will be able to understand the whole thing, et cetera. There shouldn't be any mystery in this. It almost seems like a long exercise, and there isn't anything I'd...

Feynman's approach to precision QED calculations, see his book "Quantum Electrodynamics", was shown(?) to be equivalent to the method of quantum fields. Both methods get the right the get the right answers to some problems. What quantum problems does Feynman's method (there is a name for that I...

I would like to understand basic construction of entanglement "explanation" in QED. As I understand because we talk about coincidences QED explanation necessarily involves Fock states. And Fock states are expressed using annihilation and creation operators, right?

The classical problem of radiation reaction classical electrodynamics seems to be a huge mess with no good answer. There is no even consensus of the very form of the Newton law "predicted" theory. So, the question of this thread is: Does the classical limit of QED say something about this...

Hi physicists , I'm in high-school yet, and since I've started study physics for myself my aim is to understand more complex fields of physics, and one of these fields in QED(Quantum Eletrodynamics) and QCD(Quantum Chromodynamics), could anyone tell me what the path to go for a good basis for...

I think I have found a mistake/wrong formulation at Peskin’s, when he discusses the renormalization of QED. In particular, he defines the 1PI of the electron’s self-energy on page 331 as: –i\Sigma( \displaystyle{\not}p ) and the corresponding counterterm on page 332 as: i(...

Hi, i have some trouble with feynman rules after wick's rotation. I don't understand how the propagators transform. In particular if i take the photon's propagator in minkowskian coordinates i don't understand where the factor "-i" goes after the transformation. ## \frac{-i\eta_{\mu\nu}}{p^2}...

I have been reading Richard Feynmans Quantum Electrodyamics and quite early in the first chapter he asserts that Photons are particles. His reasoning that as you decrease the intensity of light incident on a photomultiplier the clicks which the multiplier make become less frequent but equally...

From a conceptual point of view, how is it that Quantum Electrodynamics explains the interaction between two charged particles, (let's say two electrons)? I've heard people say that the electrons exchange photons, but how is it that an electron would know when to send off a photon and that it...

I'm relatively new to QFT and was wondering how the QED vacuum has a dormant zero average-field condition if there is a zero-point energy of the field as well? How is there a zero average and a zero point energy?

The Purcell effect is when an atom placed inside a high finesse cavity with a very small mode volume gets an increase in the spontaneous emission rate. I've tried to find correct explanation for this effect, but it seems hard to find, except that it comes from an increase in the vacuum density...

Hi there, I have a question about the definition of a charge of a free electron. Let's suppose that QED is the true theory of the interactions of charged particles. Presumably the charge on an (effectively) free electron, then, is the charge on an electron in which the electromagnetic...

Studying the production of the bound state of ##μ^+μ^- ## in the scattering experiments of ##e^+e^-## at electron positron colliders ##e^+e^-\toμ^+μ^- ## via ##e^+e^-\to 2γ\toμ^+μ^- ##. This bound state further can decay into ##e^+e^-## or ##2γ##. I am confused about the vertex ## 2γ\toμ^+μ^-...

I read that a wave function of the photon does not exist in coordinate space. But, when I read Feynman's "QED: the strange theory of light and Matter", for instance, when the photons travel through the glass, it seems like wave functions of photons. How it is with this?

As a rule of thumb, we might say that quantum theory becomes essential when we're analyzing systems at small distances (of the order of atomic sizes or less) and few enough particles (suppose particle number is conserved, as in QM); however, the world as a whole is quantum, and even a system...

To my understanding, QED is about electromagnetic interaction, and in a solid system, the interaction is only electromagnetic So why there are stills lots of research in solid state physics ? Is there something not explained by QED ?

First I would like to say that I'm sorry if this question has been asked before- I'm new here. I was reading QED by Richard Feynman, and he mentioned that any given antiparticle is just it's regular particle counterpart moving backwards in time. How is this possible? I thought that it was only...

Hi, In QED it is stated that an EM field can be written as a sum of quantized oscillators (the photons). In "classical" Electrodynamics, it can also be shown that the EM field decomposes into normal modes. But both the quantized oscillators (in the Heisenberg picture) and the classical normal...

The measured energy density of the vacuum has a disturbing discrepance with the one theorized by imposig Poincare invariance in QFT, usually referred to as the "vacuum catastrophe". On the other hand the Heisenberg indeterminacy principle leads to a nonzero vacuum expectation value for the...

In the process $$e^+e^- \rightarrow \gamma \gamma$$ for which the amplitude can be written as: $$M= \epsilon^*_{1\nu}\epsilon^*_{2\mu}(A^{\mu\nu}+\tilde{A}^{\mu\nu})$$, where $$\epsilon_i$$ is the polarization vector of a photon. How can one find the tensors $$A^{\mu\nu}$$ and...

My book says that in this case $$e^+e^- \rightarrow \gamma \gamma $$ gauge invariance requires that $$k_{1\nu}(A^{\mu\nu} + \tilde{A}^{\mu\nu})=0=k_{2\mu}(A^{\mu\nu} + \tilde{A}^{\mu\nu})$$ Please see attachment. My question is how does this statement hold?

Homework Statement Write the momentum space integral representation for the following diagram in QED Homework EquationsThe Attempt at a Solution [/B]...