Feynman Definition and 649 Threads

I did not find wikipedia article to be quiet intuitive. Any online sources or your own descriptions. I would be greatful.

Are the Feynman diagrams still applicable to more than two particles interactions? This would be very helpful in modelling many-body scattering cross-sections.

Hi, the breaking radiation emitted by the scattering of an electron with an external field is described by the hamiltonian: H=\bar \Psi^- (\displaystyle{\not}{A}_e + \displaystyle{\not}A) \Psi^+ where A_e is the external static classical field, while A is the quantized field. The...

In 15-4,Feynman tried to explain why the rod perpendicular to the motion does not shrink."How do we know that perpendicular lengths do not change? The men can agree to make marks on each other's y-meter stick as they pass each other.By symmetry, the two marks must come at the same y- and y'-...

In 2-5, an analogy is given for electromagnetic field: two corks in water, and the effect of jiggling one cork on the other (probably the up and down motion). Now, that sounded more like water is a medium propagating the energy. But the electromagnetic waves require no medium for propagation...

TEDxCaltech was an event at Caltech where invited speakers gave talks in honor of Richard Feynman. The speakers are experts in the fields of biology, physics and nanotechnology. Among the speakers are Leonard Susskind, Scott Aaronson, Sean Carroll and more. I can't even say which of the...

Hi, this is probably very simple but what is the difference between these two Feynman propagators: \frac{i}{q^2-m^2} \frac{i(p/+m)}{p^2-m^2} E.g. Is one used for the invariant amplitude and the other for loop integrals? Or is one for a fermion and the other for a boson? =s Thanks!

in chapter 32 section 4 on electromagnetic waves, near the end he writes since \lambda = \frac{2\pi c}{\omega} then \Delta\lambda = \frac{2 \pi c \Delta \omega}{{\omega}^2}. i understand the first equation he writes but then the second one i am having trouble convincing myself how he came up...

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...

Homework Statement For a real scalar field \phi, the propagator is \frac{i}{(k^2-m_\phi^2)}. If we instead assume a complex scalar field, \phi = \frac{1}{\sqrt{2}} (\phi_1 + i \phi_2), where \phi_1,\phi_2 are real fields with masses m_{\phi 1},m_{\phi 2}, what is the propagator...

Please teach me this: Does a symmetry of Lagrangian be reserved in each Feynman diagram of perturbative QFT,because even Ward Identity still deduces from U(1) symmetry that we consider each diagram has?. By the way, does effective action reserve the symmetry that Lagrangian has?. Thank...

I'm trying to do the following problem: ie. I'm trying to use the Feynman rules for momentum space to write down the mathematical expression that the diagram is supposed to represent. However, I don't feel very confident in what I've managed so far. Now as I understand it, these diagrams...

Homework Statement I need to construct the Feynman loop integral for the following diagram: (*) where \nuL is the left-handed neutrino, \phi is a scalar particle and N is a heavy neutrino with a Majorana mass. Homework Equations N/A The Attempt at a Solution I'm trying to determine it...

There are all these Feynman YouTubes. Does anybody have a full listing? Or a favorite 10 or 20 of them? Can you list them with suggestive topic names to make it easy to find one you want? Feynman is more than physics. I'll try to start the list Different ways of thinking (counting and...

This seems to contradict the very tools we use to perform the scientific method. Immediately after performing any experiment, the measurement becomes a historical event, and this says that we cannot say that any historical event has actually occurred. Thus, I cannot actually say that I...

The Feynman slash \slashed{a}=\gamma^\mu a_\mu maps a four-vector a to its Clifford algebra-representation. This is a linear combination of the gamma matrices with the components of a acting as expansion coefficients. What physical significance does this new object have? The gamma...

Homework Statement With the time evolution time operator, where there is time dependent hamiltonian, show the new form of the feynman propagator between two states. Consider the Weyl Integral. 2. Equations from \newcommand{\mean}[1]{{<\!\!{#1}\!\!>}}...

Can someone refer me to Feynman rules for electroweak interactions in the general case of SU(2) multiplets of weak isospin n and weak hypercharge Y interacting with EW gauge bosons? I can only find the standard rules for SU(2) doublet electron - neutrino. Thanks!

Can someone describe the Feynman diagram for the Sigma plus decay to a positive pion and a neutron? I'm fine with the primary decay to the neutral pion and a proton. There appears to be insufficient down quarks created.

Hi, I am wondering how different the Feynman Lectures editions are. I have the option of getting the 1964,1965, 1970, and 1989 editions. Obviously getting the latest of those editions is the best, however I heard that the 2005 edition is the best edition with all the corrections and the one...

Hi, what do you think are the most important Feynman diagrams (or probably better: what do you think are the most important processes in particle physics)? Thanks, Quantum Cosmo

I'm reading Feynman Lectures on Physics Volume 2 Chapter 39 on elastic materials. Equation 39.22 relates the elements in the elasticity tensor to the Young's modulus and the Poisson's ratio. I have no clue on how to get these relations myself. For example, for C_xxxx, I think it should tell...

Hello, all. My colleagues and I are currently working on an exercise book for The Feynman Lectures on Physics (FLP). This book will include about 1000 exercises from the original Feynman Lectures course as taught at Caltech, covering pretty much the entire range of topics in all three volumes...

In the subject accelerometer (see link) the answer given is a = kgx. I get a = 2kgx. I'm wondering if anyone cares to discuss this problem. The answerer used an energy argument that I'm not sure I followed, whereas I used a simpler force-balance method. F = force on bead by parabola and is...

Hi all, I've been reading the Feynman Lectures on Physics and I've stumbled on something. I understand the theory but not how they arrived at the answer. It's to do with firing a bullet from a gun and working out the speed it would need to travel in a curve around the Earth's surface in order...

Hi all, I'm trying to calculate the Feynman Rules for the effective electroweak chiral Lagrangian. For example, this is the first term in the Lagrangian: \begin{eqnarray} \mathcal{L}=\frac{v^2}{4}\text{Tr}(D_{\mu}U D^{\mu}U^{\dagger}) \end{eqnarray} where \begin{eqnarray}...

Homework Statement I need to find the Feynman diagram of the transmutation of a K0 particle (one anti-strange quark and one down quark) into its anti-particle (one strange quark and one anti-down quark). Homework Equations / The Attempt at a Solution s- has a charge of +1/3, d has a charge...

I am reading Srednicki's Quantum Field Theory recently. I have thought over the descriptions of the Feynman Diagrams on his book in chapter 9, but I still can not understand what these diagrams mean and how do they help us to calculate the right-hand side of the equation 9.11 on the book. Is...

I would challenge the tradition of viewing Bohr as the most important quantum physicist. I think all of the modern physics, in a nutshell, is "relativistic quantum field theory". Thus, we need to choose between two people: the author of Lagrangian formulation OR the author of Hamiltonian one...

Does anyone want to try "Feynman tea"? I never read the book "surely you are joking mr Feynman", but I hears the story behind the title. In particular, I was told there was an episode where someone asked Feynman if he wants milk or lemon in his tea, and he said both. Then they responded "surely...

Question 1: solved! Question 2: Why it's zero? I think we cannot get zero unless it's an exact differential form? Many thanks.

I am just inhaling "The Grand Design" and am stuck in the chapter on the "buckyballs" double slit experiment. The authors say that in case of the experiment, a particle may take any possible way ("perhaps to Jupiter and back"), which then Feynman depicts as adding vectors to a result vector...

At the beginning...WOW what a huge boost in confidence! "You ask me if an ordinary person studying very hard would get to be able to imagine these things as I imgaine them? Of Course! I was an ordinary person who studied hard." ^.^ <3 I am in loveeeee...

Hey, I'm trying to do exercise I.2.1. from Zee's QFT in a nutshell but I ran into a problem. The exercise is to derive the QM path integral with a Hamiltonian of the form 1/2 m p^2 + V(q). In the textbook he shows the proof for a free hamiltonian. He gets to a point where he has (I left out...

Feynman makes an example (15-6 in his lectures) about failure of simultaneity at a distance, using the Lorentz's transformation of time. A man moving in a spaceship (system S') synchronizes two clocks, placing them at each end of the ship, by a light signal sent from the middle of the ship, and...

I just took Electromagnetism and I want to solidify my understanding of the material. I want to order the Feynman Lectures, but I've heard some complaints about different editions (unnecessary edits, quality of print, etc...). Which edition(s) is the best? Also, should I get the audio tapes...

I'm reading QED. At first I thought I understood Feynman diagrams, but due to ones like these I'm not so sure anymore. In either of these diagrams, the photon "curves" around in space time. Why would it travel in anything BUT a straight line if nothing is influencing it? I liked to picture these...

How does Feynman "Sum Over Histories" make sense? Hi. I am new to Quantum Physics and this forum as well. I was reading The Grand Design, by Stephen Hawking, and came upon the "Alternative Histories" theory in Quantum Mechanics. My questions are: 1.) How is it possible that a particle can...

Hey there, this isn't a homework / coursework question so I didn't think it should be posted in that section. I can't seem to find a source which explicitly tells you how to determine which bosons are used in reactions. I understand how to work out if a reaction is legal or not by using charge...

Consider question 1 in this paper: http://www.maths.cam.ac.uk/postgrad/mathiii/pastpapers/2002/Paper65.pdf How do we "read off" the Feynman rules? I can see that the interaction terms give contributions \lambda_3 , \lambda_4 , \lambda_6 to the relevant 3,4 and 6 point vertices respectively...

A fitting http://www.ted.com/talks/leonard_susskind_my_friend_richard_feynman.html?utm_source=newsletter_weekly_2011-05-17&utm_campaign=newsletter_weekly&utm_medium=email" by Leonard Susskind who really knew Dick Feynman. Enjoy... Rhody... :biggrin: Left me with a warm fuzzy feeling (no pun...

Consider equation 5.46 in these notes: damtp.cam.ac.uk/user/tong/qft/qft.pdf (i) why does only one term have the i \epsilon in it? I thought this was because the (p-p')^2-\mu^2 term can never vanish but this doesn't make sense since the \phi particle will have momentum p-p' and since momentum...

I'm not always on the same computer, often times I'm using my phone to look for answers when doing physics on the go. Does anyone know a good, correct resource for ALL of the tree level feynman rules for QED+EW+QCD? Feynman gauge would be preferred, or ungauged. I can find most for the...

I was bored last night and look at Wikipedia's article on Feynman when I saw this quote: http://en.wikipedia.org/wiki/Richard_feynman#Challenger_disaster (bottom of top paragraph) Can anyone put this into some context and explain what he was talking about?

Homework Statement So, I got this task, which I feel either really dumb, or nobody is able to explain: I got this question: Z and W was discovered in 1973 at CERN, how were they produced? Include Feynman diagram and a short description. Then there is this question: How is the Z and W produced...

I have drawn up what I believe happens during electron excitation in an atom. However, it looks very... wrong somehow. My diagram shows an elestron moving in time but not space until it is hit by a photon, after which it disappears and instantly reappears at a higher energy level. After some...

Hey guys, say i have some standard propagators then I know how to combine them using Feynman's parameter method. But what do I do if one of these propagators is linear? For instance: \int d^Dk \frac{1}{(k-p)^2(k \cdot q)} where q and p are some momenta. How do I combine them? Does...

http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf Consider the Feynman rules for Green's Functions given at the top of p79 in these notes. Now let us consider the diagram given in the example on p78. Take for example the 2nd diagram in the sum i.e. the cross one where x1 is joined to x4...

Does anyone here use the package feynmf to generate feynman diagrams? I can use it to build diagrams, but I don't know how to build sums of diagrams i.e. diagramA + diagram B + diagram C Does anyone know how to do this? Thanks

Pardon me if this is the wrong section for this question, but "energy" seemed like a topic that could fit in almost any category on this site. Either way, I'm sure many people on here have seen this quote by Feynman: Is Feynman correct about this? Because the way Feynman puts this, it...