Feynman Definition and 649 Threads

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?

Homework Statement It is a thing feynman doesn't explain, it is meant to be obvious, but for me and some friends is not. If you have the first book, chapter 30-6, "Diffraction by opaque screen", he is talking about the approssimation of the two path: for finite distance is h^2/s, and is...

Feynman very clearly presented QED in his book The strange theory of light and matter. He tried also with quantum gravity calculations. But, how to clearly present, why his calculations did not lead to quantum gravity.

I'm working on a "draw all possible Feynman diagrams up to order 2" problem for a scalar field that obeys the Klein-Gordon equation, and I'm wondering about a few things. When I did a course on particle physics and was first introduced to Feynman diagrams in the context of QED (but not QED...

I'm probably missing something small but I haven't been able to figure this out. In the Feynman rules (for a scalar field that obeys the Klein-Gordon equation), you write a propagator for internal lines as \frac{i}{k^2 - m^2 + i \epsilon}. The propagator integrand is originally...

Say you want to evaluate this integral: \int^{\infty}_{-\infty} \frac{dx}{x^2-A} Since the bottom factors into \frac{1}{(x-\sqrt{A})(x+\sqrt{A})} , using the theorem of residues, the integral is \pm 2\pi i (\frac{1}{2\sqrt{A}}) (where \pm is + if Im \{\sqrt{A} \}>0 and - otherwise, but...

Vincent Rivasseau and four others just posted "July3150" (I mean 1007.3150, just easier to remember that way for some reason) where they made the observation in effect that spinfoams are the Feynman diagrams of GFT. It's not a new thing to point out, but it is very helpful to mention...

I have been studying how to apply the Feynman rules for QED to various simple first order process (as prescribed by Griffiths' 'Introduction to Elementary Particles'). So far, all is well. I can follow the rules, and develop the results, and it all looks very clever. My problem is that so...

hey, i want to find the lowest order strong interaction feynman diagram for the following process: \Sigma^{++}_c \rightarrow \Lambda^+_c \pi^+ the quark composition is: \Sigma^{++}_c = (c u u) \ \Lambda^+_c = (c u d). \pi^+ =( \bar{d} u ) an image of a correct process is attached...

Can anyone explain what Feynman means when he is talking of a reversible machine in the chapter four of his lectures? What exactly is a reversible machine? Please explain this paragraph : "If when we have lifted and lowered a lot of weights and restored the machine back to its original...

Whenever I see examples of the diagram for the Coulomb interaction it always seems to be two electrons interacting via an electron and being repulsed. The diagram looks intuitive in terms of momentum conservation. I was wondering how (for example) a proton - electron interaction, and...

Hello, I have read the probability chapter in Feynman's lectures on physics. And got fascinated by the random walk. There is a statement, that in a game where either a vertical distance of +1 or -1 can be walked each move, the expected value of the absolute distance (lets call it <D>) from...

I'm trying to show equation (6.39) on page 189 in Peskin & Schroeder. Homework Statement Show that \frac{1}{AB}=\int_0^1dxdy\delta(x+y-1)\frac{1}{(xA+yB)^2}. Homework Equations Defining property of Dirac delta function: \int_{-\infty}^{\infty}dx f(x)\delta(x-x_0)=f(x_0) Also...

I found this passage interesting and illuminating: (from Feynman's book 'QED') ".. In this example, complex numbers were multiplied and then added to produce a final amplitude for the event, whose square is the probability of the event. It is to be emphasized that no matter how many...

So I bought myself the Feynman lectures and was reading up on his discussion on Statistical Mechanics and Thermodynamics (in volume I). The following is regarding Thermodynamics. So he defined entropy (at least the change in it from a to b) as delta S = int(Q/T) over a reversible path from a...

I know I should know this, but I have a quick question. Let's say we have a diagram: 1-->----------2 | | <- "q" v | 3--<----------4 Lets assume: 1 = "quark" 3 = "antiquark" 2 = W boson 4 = photon q = same quark flavor as "3" Time...

Homework Statement At the Tevatron you observe the process u ̅u → τ+τ−. Draw the lowest order Feynman diagrams for the processes involved and state which interactions are responsible. Label all internal lines, external lines and vertices [u = up quark, τ = tau lepton] The Attempt at a...

Homework Statement I need to draw a series of Feynman diagrams to show some processes, but I'm unsure if I'm doing these correctly. I've put them together in this one post and detailed each below in turn, hopefully this is going to make sense. I know there's a few, but I want to make sure I'm...

I'm learning how to do Feynman diagrams for an exam coming up, and have come across diagrams in both position and momentum space. If I'm asked to draw a Feynman diagram without specifying which kind, is it generally assumed that it's in position space? If I label the the incoming and outgoing...

I have a two point Green's Function with a phi^4 interacting Hamiltonian and am considering the second order of pertubation, and must work out the following: T[\phi(x_1) \phi(x_2) \phi(y_1)^4 \phi(y_2)^4] = T[\phi(x_1) \phi(x_2) \phi(y_1) \phi(y_1) \phi(y_1) \phi(y_1) \phi(y_2) \phi(y_2)...

I have spent a while trying to get to grips with the building blocks used for constructing feynman diagrams, below is my attempt at a set of reactions, how am I doing so far? I don't think e^{+}e^{-}\rightarrow\mu^{+}\mu^{-} can happen since a gluon only interacts on particles with a...

Does the math of the Feynman path integral dictate particles taking many paths or is that just an english language gloss-over? Thanks, Jake

I ran a search for gyroscopes looking for a definitive solution to the "What causes Precession?" and found no good clear answers. I think the Feynman lectures come close to the solution and followed that thought process, all the pieces point to the solution, I had to put my theory to the test on...

Hi, Could u advise me please some references where the Feynman rules for graviton are derived I mean graviton-scalar graviton-graviton scattering ... in general graviton vertecies ... Thank you

Hi all! Does anyone know the position space representation of the Feynman propagator on the cylinder? The momentum space representation is the same as in Minkowski 2D space, but the position space representation is different because the integrals over momenta are now sums. Or could someone...