Feynman Definition and 617 Threads

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...

Homework Statement I'm asked to draw a Feynman diagram for two neutrinos scattering from each other. Homework Equations None The Attempt at a Solution I don't really get the question so I don't know what I'm actually supposed to put in the diagram. Am I supposed to draw a diagram...

Hey guys, does any of you know where I could find the Feynman rules for scalar QCD? If they where colour ordered, even better! Cheers, earth2

I'm supposed to use the relationship A^{-1}=\int_0^\infty d \alpha e^{-\alpha A} to show that \frac{1}{A_1 A_2 \dots A_n}=(n-1)! \int_0^1 dx_1 \dots \int_0^1 dx_n \frac{\delta(1-x_1- \dots - x_n)}{(x_1A_1 + \dots + x_nA_n)^n} I decided that I should try and do this inductively. So far I...

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...

I have a process that a scalar and a photon at the final state. When we take the complex conjugate and sum over photon final polarization state...it give negative sign in the differential cross section...what does this mean? the trace didn't give negative value. M=M^{\mu}\cdot\epsilon_{\nu}...

Ok so I heard that these are great and that a physics student should have them, but I don't know what version to pick. Like there's https://www.amazon.com/dp/0805390456/?tag=pfamazon01-20 And https://www.amazon.com/dp/0465023827/?tag=pfamazon01-20 So the 2nd one is newer, so maybe more up to...

but isn't a particle just an idea? like the point in geometry i guess what I'm having trouble understanding is the divide between theory and reality is explaining how a system behaves the same as saying what the system is?

Hi everybody, as usual I need help with some definitions regarding many-loop calculations. In particular what do we mean with planar and non-planar topologies exactly? I have an idea but I'm really not sure how to formalize it for an arbitrary big number of loops and legs. Second, once...

Hi, So if we have an interaction Lagrangian for a Majorana field: L_1=\tfrac{1}{2} g\phi\Psi^{T}C\Psi Now looking at the path integral, I believe this must go like: Z (\eta^{T},J) ~ \exp{[\tfrac{1}{2} ig \int\,\mathrm{d}^4x (\tfrac{1}{i}\tfrac{\delta}{\delta J(x)...

In a Feynman Path integral, Z(\phi) = \int \cal D \phi e^{\frac{iS(x)}{\hbar}}, what does the object e^{\frac{iS(x)}{\hbar}} mean?

I am getting ready to go back to school for physics this coming fall, but in the mean time I am doing a lot of study on physics materials simply because I find it absolutely fascinating and do not want to wait however many months (Not to mention how long it will take me to get past classical...

Could somebody please explain this excerpt to me from Feynman's Lectures on Physics on perpetual motion? I don't completely understand his definition of perpetual motion. Thanks! "We must be careful to define perpetual motion...If, when we have lifted and lowered a lot of weights and restored...

I am trying to draw feynman diagram by using LaTeX code but the label in the code do not appear in the pdf(only the diagram appear). I am using the MikTeX 2.8 in windows XP and userpackage is feynmf. I have try several time and search through the web but I can't figure out any solution for this...

I've learned a great deal through the talks and books (most of which are transcribed talks or interviews) of Richard Feynman. But a lot has happened since then. One thing I've been wanting to do is go back and take note of any time he says "But we don't know such and such yet," or "such and...

Dear users, I am dealing with the proof of the Hellman Feynman-theorem for time-dependent wavefunctions given by the Wikipedia: (http://en.wikipedia.org/wiki/Hellmann%E2%80%93Feynman_theorem#Proof_2) I got stack: \begin{align} &\frac{\partial}{\partial...

For a leptonic weak interaction diagram, we have an election converted into a neutino and emitting a w- particle. But only left handed part should undergo weak interaction. So basically you should have the left handed part of electron converted into a neutrino(left handed) emitting a w-...

Hi I need help to understand Feynman rules for decay for exams. In past paper there is the following question as whether the following are allowed. cc decays to tau++tau-. From What I can see this is possible via the strong force is this correct? The next is cc decays to cu and cu. From...

...compared to normal particles? I was told this was something about, for a particle moving forward in spacetime, its antiparticle can be considered as moving backwards in space time. but that really doesn't mean anything to me. what's wrong with putting a forward arrow on an...

I'm currently reading Griffiths book (I'm at chapter 4) on Particle physics, and I had a question about Feynman diagrams. In every "node" of a Feynman diagram, what quantities are conserved? Further, what quantities are conserved over the entire diagram?

In Volume 1 of the Feynman Lectures on Physics, Feynman derives the ideal gas law from Newton's laws of motion. But then on page 41-1, he puts a caveat to the derivation he has just completed: "We have perpetually been making a certain important assumption, which is that if a given system is in...

In the last chapter of "Feynman Lectures on Physics" part III, Feynman discusses superconductivity. I am particularly intrigued by his equations (21.19) and (21.31), and even more by (21.38). Is there any experimental evidence for validity of these equations? The question of validity of these...

I have just found out that Feynman also (re)discovered (some essential aspects of) Bohmian mechanics a long time ago, in his "Feynman Lectures on Physics" part III. Namely, in the last chapter devoted to superconductivity as macroscopic manifestation of quantum mechanics, he derives equations...

Very early on in Feynman's Lectures on Physics, he offers the example of a screwjack with a mass on it to demonstrate the conservation of energy (picture attached). He asks how much force would be needed to lift the one ton sitting on top of the screwjack. He then comes up with 1.6 pounds...

I'm working through Srednicki's QFT text, and I'm continuously vexed by the various numerical factors in diagrams and vertices, as well as the grouping of diagrams. For example, in Chapter 10 (pg 75) Srednicki treats basic \phi\phi\rightarrow\phi\phi scattering processes in \phi^3. He claims...

I seem to recall that Feynman had a nice discussion somewhere, possibly in the Feynman lectures, of why there is no such thing as gravitational shielding. IIRC it appealed to the microscopic picture of a Faraday cage and the purely attractive nature of the gravitational force. I can't seem to...

In computing the integral over past histories, does one restrict oneself to continuous paths, or does one take all possible combinations of points between the beginning and the end? If one sticks to the continuous paths, what justification is there in that?