Feynman diagram Definition and 167 Threads

Hi, I've been reading about Feynman diagrams lately and I'm trying to understand the pair annihilation diagram. The picture's here: http://en.wikipedia.org/wiki/File:Feynman_EP_Annihilation.svg I don't understand the following things about the diagram: 1. Why anti-patricles have to...

If we scatter unpolarized electrons off each other and we calculate the amplitude for electrons to scatter into final states and one photon to be emitted do we get destructive interference because the photon can be emitted by either electron? Is one photon emission suppressed in favor of an even...

Hi folks, I have been trying to get my head around dualities, and hit a stumbling block right away. Duality hypotheses are framed by thinking about perturbative expansions of interaction lagrangians ( at least when thinking about s-dualities). In such expansions, the first term is regarded as...

For a 2nd order electron-positron scattering, the following diagrams are possible: http://www.quantumdiaries.org/wp-content/uploads/2010/02/eepp-1024x228.png My question is: What is the meaning of the right diagram - is a photon created and annihilated instantaneously? how is this possible?

Below is a list of physicist I compiled, and there achievements. I have sources if you want them. Do tell me if there is any more I should add or anything I should add to their bios, thanks in advance.θ Richard Feynman (1918-1988) Developing Path Integral Formalism of Quantum Field...

the number stand for the index of particles (quarks and gluons) M=\bar{v}(p_2) ig_sT_{12}\gamma^\mu(12)u(p_1)\frac{-i}{p_7^2}\bar{u}(p_5) ig_sT_{56}\gamma_\mu(56)\bar{v}(p_6)\frac{-i}{m-\gamma^\mu p_{9\mu}}\bar{v}(p_3)...

Hey guys, I was thinking about this for a while now and I seem to be on a dead end. So here it is, this is my speculation. I would love some feedback, tell me which parts are correct/false and if they are false, guide me towards the right path! :) 1. Photons can technically be their own...

I need help :( How can I draw a Feynman Diagram, starting with a Lagrangian?

I studied string theory for 2 years officially and much more on my own, chance made it that I spent the last year reading "serious" algebraic topology books and differential geometry specific for mathematicians. After gaining this insight I am very skeptical about string theory and the...

I think that Wick theorem permits us to contract boson field operator with fermion field operator(?).Because the commutator between fermion and boson field operators is like commutator between two boson field operators.Then why in Feynman diagrams do we only consider propagators of boson,fermion...

i was just reading the following article and had an interesting thought; http://www.ipod.org.uk/reality/reality_arrow_of_time.asp Referring to the following image (http://www.ipod.org.uk/reality/reality_arrow_of_time.asp ) Both Feynman diagrams are said to be mathematically equivalent...

Would someone please tell me how I would show Strontium-90 decay into Yttrium 90(and emitting Beta particles)? Would I need to use a Feynman diagram? Thank you!

I read the book of "quantum field theory in nutshell" by A. Zee. There is a "baby problem" in Page 44. I can't understand how to get the diagrams of Figure 1.7.1 from the calculation of -(\lambda/4!)(d/dJ)^4 differentiating [1/4!(2m^2)^4]J^8. How to associate this term to the three diagrams...

I met a problem when I read the textbook "Relativistic Quantum Mechanics" by J.D.Bjorken. He said we can get the potential V(r_1,r_2)=\frac{f^{2}}{\mu^{2}}(1-P_{ex})(\tau_1\cdot\tau_2)(\sigma_1\cdot\nabla_1)(\sigma_2\cdot\nabla_1)\frac{e^{-\mu|r_1-r_{2}|}}{|r_1-r_{2}|} (10.51) from the...

I understand that Feynman diagrams can be expressed either in the position or momentum representation. Is the 4-momentum conserved at the vertices in each case or only in the momentum representation?

Hello dear everyone I would like to ask if someone can help me with the following two things: 1) How many different feynman diagrams can one possibly draw for Higgs strahlung production that is of 4th order? The mediator should be Z-particle. 2) Formulate an equation for the amplitude...

Hi i can't understand why is the positron in Feynmans diagram is going towards the w+ boson and not outward, i have a problem understanding why this is happining for beta minus decay also the antielectron neutrino is also going towards the reaction of the w- boson

Hi, I am drawing Feynman diagrams for various Higgs decay channels. There are two diagrams I am stuck on and there aren't many examples online. They are H→gg and H→Z\gamma For the H→gg decay I had a stab at drawing the reverse of the gluon fusion diagram. Higgs decaying to two gluons via a...

Homework Statement Hey guys, so I'm new to Feynman diagrams, and I have a few to draw but i'll start with the first one. I'm being asked to draw the following process: \pi^{0}(uu* or bb*)→\gamma +\gamma. I have to "clearly label each quark, lepton and boson, and say which fundamental force...

I'm trying to calculate the amplitude for an interaction between a scalar field $$\phi$$ and two identical spin 1 fields $$A_{\mu} \quad and \quad A^{\mu}$$ for the interaction $$\phi \longrightarrow A^{\mu} A_{\mu}$$ with the Lagrangian density $$L_{int} = -ik\phi A^{\mu} A_{\mu}$$ where k is a...

Can a W+ boson couple to a W- boson? Say, if a Higgs decays into a W+ and a W-, what would be the Lagrangian density for this interaction? How would you evaluate such a first order diagram?

Consider the Feynman diagram below from, http://hyperphysics.phy-astr.gsu.edu/hbase/particles/expar.html where I assume time runs upwards and the gluon in the graphic runs horizontal and is labled as a green_antiblue gluon. If the gluon runs horizontal can one still label a gluon as being...

How can we demonstrate that the symmetries of S-Matrix can be applyed to parts of Feynman diagrams?The S-Matrix is the sum of infinite diagrams,why we know each or part of each diagram has the same symmetries as the symmetries of S-Matrix?

I am studying QFT from Srednicki's book. Let me ask a question about symmetry factor from this book. Let, for specific values of V and P from eqn (9.11) we get some terms. One of them is a disconnected diagram consisted of two connected diagrams C_1 and C_2. The disconnected diagrams...

Hi all Just a basic question really; I'm at university and have been tutoring someone through a couple of A level physics modules, and I'm covering some basic particle physics at the moment, which is all alright, but I've come to an issue with Feynman diagrams. Basically, for interactions...

Homework Statement Is the following reaction possible? If so, by what force? Draw (one of, if applicable)the lowest order Feynman diagrams for the process. n + n-bar --> ∏+ + ∏- + ∏0Homework Equations N/AThe Attempt at a Solution This process, it seems to me, should be possible. It...

Would it just be the same as with two electrons? (or any other pair of particles with the same charge) I'm kinda in two minds, I suspect that is wrong because wouldn't the fact that they attract each other (instead of repelling) means that the diagram would be drawn differently?

Hello, I am trying to compute feynman diagrams with the feynman rules but I encounter some difficulties... Since the gamma matrices, spinnors, etc do not comute, the ordering of the different factor from feynman diagram has an importance. Is there some rules that say where to begin and in...

I'm reading something which highlights the Feynman rules for QED, and it talks about what happens if you go along a fermionic line. For example this picture: http://wikipremed.com/image_science_archive_68/010601_68/170750_298px-ComptonScattering-u.svg_68.jpg According to these notes, there...

Hello all . In feynman diagram horizontal direction is space . is that mean distance between particles ? is that means two electron must be near a certain distance to create a virtual photon ? Does one electron in Earth send electromagnetism force to one electron on moon by virtual photon ...

Hi all, I'm just getting started on particle physics and I have a few foolish :shy: questions about drawing feynman diagram. First, when do we draw the gauge bosons(such as W) vertically rather than horizontally through time? Second, can we always replace mediator photon by Z boson...

Hi all, I am learning Feynman diagrams, and I have a quick question: in diagrams such as the one for electron-positron annihilation (see http://en.wikipedia.org/wiki/Feynman_diagram#Electron-positron_annihilation_example) why is it that the line "in the middle" is that of an...

Looking at, say, the decay K^+ \to \pi^+ + \pi^+ + \pi^- + \gamma, is it easy to say what the Feynman diagram is of highest contribution? I suppose it is not unique, but say we're satisfied with just one of highest order. Is there as it were a sort of flowchart one follows? For example, since...

Feynman Diagram: Simga+ --> p + gamma? Hi, Can anyone give me some indications as to how to draw the feynman diagram for the following decay? Ʃ+ → p + \gamma Should I consider the quark composition of the sigma first? Thanks a lot.

Hi all After many months of contemplating, coming up with tattoo ideas, waiting a few months to see if I still like that idea, etc etc, I've settled on getting a Feynman diagram for many reasons, but having a but of trouble settling on one in particular. I've seen a few with the standard...

Hi, I'm taking introductory particle physics and this is related to the first couple of chapters in Griffiths. If I draw a Feynman diagram for a particular process, what conservation laws must hold at each vertex? Mainly looking at QED processs but as far as I can work out energy and momentum...

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

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...

Hello there, I am looking at the decays of Heavy sterile neutrinos in the their mass states to Z bosons. Using the feynman rules, how would I go about calculating the decay amplitude. I have only ever seen cases where the Z boson is a propagator. Would my expression look something like this...

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.

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...

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...

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...

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...

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-...

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...

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...

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...

I need help - Higgs for idiots: So, how a particle which have no mass without higgs (so it travels at c, and on feynman diagram we would draw its worldline at 45deg) can slow down or even be at rest when Higgs is switched on? Could anyone draw a feynman diagram?